Smartphones are expensive, yet why do their batteries degrade after a few years of use, while power banks don't seem to have similar issues?

Understanding Battery Life: Phones vs Power Banks

In essence, it’s straightforward: the cycle count of a mobile phone is significantly higher than that of a power bank, and the working conditions of a phone battery are more severe than those of a power bank.

First, let’s discuss why the cycle count of a phone is much higher than that of a power bank. In practical use, you’re unlikely to use a power bank with every charge. They are typically used only in specific situations like travel or overnight stays. Most people prefer to fully charge their phones before leaving the house, which results in a relatively low cycle count for the power bank.

However, let’s assume you always charge your power bank and then use it to charge your phone. You’ll notice that the capacity of the power bank is much higher than that of the phone. For example, a common 10000mAh or 20000mAh power bank (both at 3.7V) can charge a phone with a 5000mAh battery (a typical capacity for mainstream Android phones) about 1.2 to 2.4 times from 0% to 100% (using a conversion factor of 0.6 for simplicity). This implies that, over time, the cycle count of the phone will be significantly higher than that of the power bank. In reality, it’s even more pronounced. A phone battery might reach its end of life after nearly a thousand cycles, whereas a power bank might only go through a few hundred or even just dozens of cycles.

Our national standards require that after 500 cycles, the battery should still retain at least 80% of its capacity. Many phone batteries actually exceed this standard, with some maintaining up to 90% capacity even after a thousand cycles. However, the significantly higher cycle count compared to power banks can make phones seem less durable.

The second issue is the harsh working conditions for phone batteries. Unlike power banks, which only experience wear from charging and discharging and heat generation, phone batteries are frequently exposed to temperature environments that can damage them. For example, why do phones discharge more quickly in winter? As I mentioned in a previous answer:

Compared to low temperatures, high temperatures are more dangerous because they can cause irreversible damage to lithium batteries. Exposure to high temperatures, such as near high-heat devices, inside a phone near the motherboard, or in a car on a hot day, can trigger unintended chemical reactions that reduce battery capacity or even pose safety risks. Phones have their batteries close to the motherboard and other heat-generating components. During intense use (like gaming or video recording), the external temperature of the phone can reach 45 degrees Celsius, and the internal conditions for the lithium battery are even harsher.

The optimal storage temperature for lithium batteries is between 0-40 degrees Celsius, and they should ideally operate below 35 degrees Celsius. This is achievable for power banks but almost impossible for phone batteries, even if they are not cycling and are constantly connected to a charger. These conditions can damage the battery, reducing its lifespan and overall endurance, which is not surprising.

The toxicity cannot be discussed without considering the dosage.

The main reason why the battery of a mobile phone deteriorates faster than that of a power bank is that the charging frequency of the phone is much higher. Therefore, within the same period, the phone is charged far more times than the power bank.

Differences Between Mobile Phone Batteries and Power Bank Batteries

The working environment and usage frequency of power bank batteries and mobile phone batteries are different, leading to differences in their lifespans.

Mobile phone batteries are charged more frequently. Nowadays, people are inseparable from their phones - they use them during meals, in the restroom, and even while sleeping, causing many to suffer from battery anxiety. Seeing anything less than 100% battery on their phones triggers the urge to charge, especially for heavy mobile gamers who might charge their phones multiple times a day. Power banks, on the other hand, do not face this issue as they generally have larger capacities.

Additionally, power banks are not subjected to high temperatures like phones. The CPU in a phone, especially during complex computations, generates significant heat, and since the battery is inside the phone, it can be exposed to high temperatures. In the case of gaming phones without proper cooling, the back of the phone can reach temperatures of 40-45 degrees Celsius or higher, which can adversely affect battery lifespan and battery life. However, power banks do not experience this level of heating during phone charging, and it does not impact battery lifespan or battery life.

Furthermore, power banks do not need to be held in hand constantly. They are usually kept in bags or pockets, which means their battery reserves are not affected, even in cold weather. In contrast, holding a phone in hand all the time can lead to reduced battery life.

Both mobile phones and power banks use lithium-ion batteries, which have a specific operating temperature range, typically between 0°C to 35°C. Going below or beyond this temperature range can affect battery life. In cold temperatures, the chemical reaction rate in lithium-ion batteries decreases, leading to reduced battery life.

Lithium-ion batteries, also known as rechargeable batteries, are widely used in modern digital electronic devices. They differ from lithium batteries in that they use lithium-containing materials (graphite and petroleum coke) as electrodes, which significantly reduces the reactivity of lithium and solves safety issues present in traditional lithium batteries.

While lithium-ion batteries offer many advantages, they also have notable drawbacks. Advantages include high energy density, longer storage time with low self-discharge rates, long charge cycles (around 500 to 1000), and no memory effect, allowing them to be charged at any time.

Battery Degradation: Mobile Phones vs. Power Banks

The most significant factor affecting battery degradation is the number of charge and discharge cycles, a characteristic stemming from the changes in the lithium-ion insertion and de-insertion mechanisms.

The working principle of lithium-ion batteries is based on the movement of lithium ions between positive and negative electrode materials. During charging, lithium ions move from the positive electrode and embed themselves in the negative electrode, while during discharge, lithium ions de-insert from the negative electrode and return to the positive electrode. As the number of cycles increases, the electrode materials undergo microscopic structural changes, affecting the efficiency of lithium ion insertion and de-insertion, ultimately leading to decreased battery capacity.

So, as long as it’s a lithium-ion battery, this fundamental principle remains unchanged.

Power banks, however, perceive this issue less prominently, and there are two main reasons for it:

**1. Charging frequency: Power banks are generally not charged as frequently as mobile phones. Charging a power bank to full capacity every day and using it again at night, as opposed to charging a mobile phone multiple times a day, is much less common. For instance, my own power bank might not need charging for a week. Don’t underestimate the difference in charging frequency over the course of a year. Additionally, power banks can completely avoid the issue of using while charging.

  1. Battery capacity: Power banks typically have larger capacities, with 10,000mAh being a common mainstream capacity. Even when this capacity is slightly exaggerated (usually by 10% to 20%), it’s unlikely to be noticeably affected by the gradual degradation that accumulates over time.**

In fact, the lithium-ion batteries used in regular power banks are not as advanced as those found in mid to high-end smartphones, which can be seen in examples of faster degradation when third-party batteries are used. However, battery technology has not seen a significant leap, especially in terms of energy density, resulting in relatively modest improvements in perception.

In the near future, solid-state batteries could alleviate some of these issues. They have a more stable structure, and their electrolytes are less prone to degradation. If better electrode materials can be developed, it would be even more beneficial. In the automotive industry, high-end vehicles already widely use solid-state batteries.

Industry reports also suggest that in 2024, the focus for smartphones regarding battery life will likely shift away from increasing charging power and speed. The marginal effects of charging speed have begun to diminish, with many people feeling less impressed by 100W, 150W, or 200W charging compared to the previous jump from 10W to 50W. However, increasing battery capacity by a few hundred milliampere-hours would provide a much more reassuring improvement.

Another drawback to consider is that while smartphones can cost thousands of dollars, the cost of the battery component is not particularly high and accounts for a relatively small percentage of the overall cost, making it seem somewhat disproportionate.

Battery Lifespan: Mobile Phones vs. Power Banks

You may be using power banks with capacities ranging from tens of thousands to even tens of thousands of milliampere-hours (mAh). These power banks are similar in size to mobile phones but have much larger battery capacities, whereas mobile phone batteries typically have capacities of around 5000mAh. As a result, the difference in lifespan between mobile phone batteries and power bank batteries is primarily attributed to significant differences in usage frequency and the number of charge and discharge cycles.

!{20,000mAh Power Bank with Fast Charging}

Mobile phones, as everyday devices, constantly operate either in a charging or discharging state due to their high usage frequency. Typically, when going out, they need to be charged midway (I should mention that I use a device with a battery capacity of 5500mAh when I go out, and it hardly requires recharging). In contrast, power banks are used less frequently, often only in specific scenarios like outdoor travel or office trips, and one power bank can charge multiple devices. This difference in usage frequency results in distinct battery lifespan performance between the two.

!{5000mAh Mobile Phone Battery}

As mentioned earlier, power banks generally have battery capacities several times larger than mobile phones, creating a larger buffer zone and the ability to withstand more charge and discharge cycles. Mobile phone batteries, on the other hand, have limited charge and discharge cycles due to their relatively smaller capacity, leading to a gradual decrease in battery capacity over time. Therefore, even if your power bank’s battery capacity decreases, you are unlikely to notice it. For instance, going from 20,000mAh to 10,000mAh would still easily allow you to charge your phone twice.

!{20,000mAh Power Bank}

Additionally, mobile phone batteries are affected by other factors, such as the trend towards larger battery capacities in newer phones and increased overall power consumption, both of which contribute to a reduction in the battery life of older phones. While power banks theoretically have a longer lifespan, there doesn’t seem to be precise industry standards for their actual lifespan. Different brands and qualities of power banks can also vary in battery lifespan. Therefore, even with the same 20,000mAh capacity, the difference in quality might mean the ability to charge three or four phones, but users are unlikely to perceive this difference because, on a full day out, charging your phone two to three times is more than sufficient.

In conclusion, although both mobile phones and power banks use lithium-ion batteries, the differences in usage frequency, charge and discharge cycles, and other factors result in mobile phone batteries showing significant signs of wear and tear after several years of use, while power bank batteries experience relatively fewer such issues (although they may exist but are not easily noticeable).

Battery Comparison: Power Banks vs. Mobile Phones

In reality, both power banks and mobile phones use “Lithium-ion batteries," and their “charging and discharging principles” as well as “lifespan” are quite similar.

The reason some people perceive that mobile phones drain battery faster while power banks are more durable primarily stems from the differences in their “usage habits."

Typically, lithium-ion batteries can endure approximately 500-800 charge and discharge cycles. Mobile phones, being daily drivers, are constantly in either a charging or discharging state, given their high usage frequency. Charging your phone daily is a common practice for most of us. With this regular charging pattern, after about two years, your phone’s battery naturally starts deteriorating. In fact, you might notice a drop in battery efficiency within the first year of using a new phone.

On the other hand, power banks are designed as dedicated power sources for mobile phones and tablets. They come with larger capacities and can charge a phone multiple times in one go. Therefore, the frequency of use for power banks hardly matches the daily charging routine of a phone. Consequently, their lifespan is relatively longer. Additionally, power banks have larger capacities, often exceeding 10,000 milliampere-hours (mAh), while mobile phones typically have batteries below 5,000mAh. Comparing the two is like comparing apples to oranges, as larger capacity results in more buffer room, allowing for greater longevity. Lastly, ask yourself, do you use your power bank every day, or does it sit unused for extended periods? This, too, contributes to why power banks can last a long time if well-maintained.

However, it’s worth noting that it’s not recommended to use the same power bank for several years without any issues. Generally, after about two years, consider replacing it to ensure charging efficiency, stability, and to minimize potential safety hazards such as internal voltage device aging or water damage.

How to Extend the Lifespan of Your Mobile Phone?

Adopting the correct usage habits and charging practices can help extend the lifespan of your mobile phone.

Avoid overnight charging. Charging your phone is not a case of the longer, the better. For batteries without protection circuits, it’s essential to stop charging once it’s full to prevent overheating or performance issues, especially when charging overnight.

Consider the charging environment (avoid charging in high-temperature or high-humidity conditions). Stable temperature conditions are necessary for the charge and discharge process of phone batteries. Extreme temperatures, whether too high or too low, can affect charging efficiency and lead to phone problems. For instance, during hot summer days, avoid charging your phone in direct sunlight, and don’t place it in an environment with excessive air conditioning. Ideally, charge it at room temperature.

Choose an adapter with the appropriate voltage. Different chargers have varying current efficiencies, ranging from 5V1A to 120W fast charging. Therefore, it’s crucial to ensure that the charger is compatible with your phone model. It’s advisable to use the original charger whenever possible.

Avoid using the phone while charging. Some users have the habit of using their phones for activities like watching videos or gaming while it’s charging. This can easily damage the phone battery’s lifespan because during charging, the phone’s circuit board generates heat, and combined with usage-induced heat, it can lead to overheating.

Turn off power-hungry applications to extend battery life. In daily use, you can control the permissions of applications for auto-start and background processes within your phone settings. This ensures the cleanliness of your phone’s system and reduces the drain caused by power-hungry apps.

Follow @张庸白 for more insightful tech knowledge!!

Understanding Battery Degradation and Why Power Banks Fare Better

This is a lithium-ion battery.

The principle behind lithium-ion batteries involves two electrodes separated by a separator. The electrodes are known as the cathode (positive) and anode (negative), with the battery containing an electrolyte filled with lithium ions (Li+). Charging involves moving lithium ions from the anode to the cathode, while discharging moves them from the cathode to the anode.

In essence, it’s somewhat analogous to storing potential energy in a hydroelectric dam. When there’s excess electricity, water is pumped to the dam for storage. When power is needed, water is released to generate electricity using gravitational potential energy.

During charging, external voltage prompts lithium ions (Li+) within the battery to move to the right (→). The anode on the right, typically made of layered carbon, contains numerous micropores where lithium ions become embedded. This is where the concept of graphene comes into play. Once charging is complete, due to the differences in the circuitry, even though the right side has a higher potential, the lithium ions (Li+) are blocked by the separator.

Discharging involves closing the circuit, prompting lithium ions (Li+) within the battery to move to the left (←), completing the discharge cycle.

The sizes of the positive and negative electrode containers match, as they need to accommodate an equal number of lithium ions (Li+), and the battery’s capacity is determined by the smaller of the two containers. For example, if the positive electrode can hold 100 lithium ions (Li+), but the negative electrode can only accommodate 10, even with further charging, only those 10 ions can participate.

As the battery is used, wear and tear inevitably occur. It could be due to repeated activity on either side, and occasionally, a lithium ion (Li+) may become firmly bound to the active material, rendering it permanently inactive. Think of it as a romantic connection where two individuals become inseparable, unable to be separated again. This results in reduced storage capacity on one side, and fewer lithium ions (Li+) available for movement.

Comparing this to the hydroelectric potential energy example, if there’s less water in the dam, the dam’s height decreases, and the reservoir becomes smaller.

This process doesn’t occur without cause and generally happens during the charging and discharging cycles. This is why industry standards dictate that after 1000 charge cycles, the battery should retain at least 80% of its initial capacity.

For most people, 1000 cycles translate to around two to three years of usage.

Why Don’t Power Banks Face These Issues?

The majority of people follow routine routes from home to work, with minimal deviations such as school drop-offs, occasional mall visits, or infrequent travel.

In such scenarios where charging is readily accessible at home and work, how often do we actively use power banks?

Power banks are designed for situations when you’re out and about, lacking charging options, essentially serving as emergency blood bags.

Moreover, the current battery capacities in mobile phones typically hover around 5000mAh, while power banks often exceed 10,000 or even 20,000mAh. A phone may have undergone nearly a thousand charge cycles over the course of a year, whereas a power bank may only experience a single charge cycle.

A year goes by, and the phone has endured almost a thousand charge cycles, while the power bank might have completed just a hundred charge cycles or even less, considering it hasn’t been used. No usage means no wear and tear, which naturally preserves the battery’s condition.

Understanding the Discrepancy in Battery Lifespan Between Power Banks and Smartphones

This is actually a cognitive bias resulting from differences in usage scenarios and frequency.

Power banks, like smartphones, also use lithium-ion batteries for power supply. Their charging and discharging principles are the same, and they are subject to the physical properties of lithium-ion batteries. Under equivalent technical conditions, there won’t be a significant difference in their lifespans; both can degrade and swell.

Charging also has its lifespan issues.

1. Difference in Cycle Counts

The reason you might have this perception is because, in your usage scenario, the smartphone battery undergoes far more charging cycles than the power bank battery.

Let’s take a typical daily usage scenario as an example. Assuming your smartphone completes one full battery cycle every day, and your power bank completes one full cycle every five days (note that it’s full cycles, not charging frequency). Over a year, the smartphone battery would complete just slightly more than 365 full cycles because some days, with intensive use (playing games, taking photos, etc.), the smartphone might go through more than one cycle.

In contrast, the power bank would only complete around 73 full cycles in a year, which is a fivefold difference!

Power banks are designed for emergency power supply when you’re on the go, without convenient charging options. They serve as backup energy sources. Moreover, current smartphone batteries typically have capacities of around 5000mAh, while power banks often exceed 10,000 or even 20,000mAh. After a year, the phone may have gone through nearly a thousand full charge cycles, while the power bank might have completed just a hundred or even less, considering it hasn’t been used. No usage means no wear and tear, which naturally preserves the battery’s condition.

Battery cycle count impact on battery capacity

Currently, smartphone battery lifespans have improved somewhat due to technological advancements. However, smartphones are high-frequency necessities in people’s daily lives, so it’s still common for smartphone batteries to become less durable after 2-3 years.

2. Proliferation of Fast Charging for Smartphones

High-rate charging and discharging can also affect lithium-ion battery lifespan because the anode and cathode experience volume changes during these processes. The higher the charging and discharging current, the more intense the volume changes and stress, making it more likely for the anode and cathode particles to break or detach from the current collector, accelerating cycle degradation.

Additionally, the heat generated during fast charging also impacts lithium-ion battery lifespan.

Fast charging for smartphones nowadays typically exceeds 60W, with 120W not uncommon on many devices. In contrast, most power banks available in the market offer input and output power of around 20W for products in regular price ranges (fast charging power banks in the low hundreds are not uncommon either). When comparing the two, even with the same usage frequency, power banks will experience slower battery degradation.

It’s worth noting that the impact of fast charging on smartphone lifespan becomes noticeable after a long-term, high-cycle scenario, generally exceeding 800-1000 cycles, which corresponds to 2-3 years of usage.

Data comparison by He Tongxue

3. Differences in Completing Full Cycles

Completing a full cycle can impact lithium-ion battery lifespan, and power banks, due to their significantly larger capacity compared to smartphones (2-3 times or more), face a higher level of difficulty in completing a full cycle. Over time, this difference accumulates and results in a noticeable gap in lifespan.

In conclusion, the longer lifespan of power bank batteries compared to smartphones is simply a result of differences in usage frequency because both are governed by the laws of physics.

Understanding Lithium-Ion Battery Basics

To grasp this issue, it’s essential to have a basic understanding of lithium-ion batteries.

Both Smartphone Batteries and Power Banks Use Lithium Polymer Batteries

The working principle of lithium-ion batteries involves lithium ions moving between the positive and negative electrodes through an electrolyte. Charging involves lithium ions moving from the positive electrode to the negative electrode, while discharging involves their movement in the opposite direction.

One complete cycle of a lithium-ion battery refers to the entire process where all lithium ions undergo a full charge and discharge cycle, also known as one cycle period.

However, it’s important to note that many people have the misconception that “one charge equals one lithium-ion battery cycle."

In reality, one lithium-ion battery cycle equates to the cumulative discharge of the battery reaching 100%.

Let’s illustrate this with an example:

If you start charging when the battery is at 50% capacity, and then use it until it’s at 50% capacity again, this usage accounts for only 50% of a battery cycle. To complete one full battery cycle, you’d need to repeat this process. In other words, calculating the lithium-ion battery usage cycle is based on the cumulative charge and discharge of the battery, rather than considering each individual charge or discharge as a full cycle.

Of course, if you consistently use the battery from 0% to 100% and then charge it back to 100% every time, you can calculate it based on the number of charge cycles.

What Happens When a Lithium-Ion Battery Reaches Its Cycle Limit

The lifespan of a lithium-ion battery for 500 cycles refers to achieving around 625 full recharge cycles under constant discharge depth (typically around 80%). It means reaching 500 complete charge and discharge cycles (500 ÷ 80% = 625).

Furthermore, this specified cycle count doesn’t mean the battery becomes unusable after reaching this limit; it indicates that the battery’s capacity to store energy has decreased to a certain level. Generally, lithium-ion batteries can maintain at least 60% of their nominal capacity after 500 full charge cycles, while silicon anode batteries can maintain at least 80%.

When the battery’s energy storage capacity drops below 60% of the nominal capacity, its energy storage performance weakens, typically resulting in reduced standby time and lower stored energy.

In simpler terms, the internal chemical reactions in lithium-ion batteries become less active, leading to slower charging and reduced available capacity.

This phenomenon is not limited to smartphone batteries and power banks; currently, the electric vehicle industry is the sector most affected by lithium-ion battery cycle limitations.

Why Do Smartphone Batteries Degrade Faster Than Power Banks, and How Does It Compare to Electric Vehicles?

Let’s use electric vehicles as an example to explain battery degradation complaints.

In terms of battery degradation complaints, electric vehicle operators > smartphone users > power bank users.

This situation doesn’t imply that electric vehicle batteries are inferior to smartphone and power bank batteries. Instead, it’s determined by the frequency of charging and discharging of the batteries used.

Typically, electric vehicle operators need to charge their vehicles daily, sometimes even twice a day. Especially in northern regions during winter, lithium-ion batteries experience significant performance degradation in cold temperatures. Many vehicle owners need to charge their vehicles multiple times a day, even if the vehicle is parked outdoors.

  1. In low-temperature environments, the viscosity of the electrolyte increases, and in some cases, it even partially solidifies, leading to decreased electrical conductivity in lithium-ion batteries.
  2. The compatibility between the electrolyte and the negative electrode and separator deteriorates in low-temperature environments.
  3. In low-temperature environments, lithium-ion batteries experience severe lithium precipitation on the negative electrode. The resulting metal lithium reacts with the electrolyte, leading to the deposition of products that increase the thickness of the solid electrolyte interface (SEI).
  4. In low-temperature environments, the diffusion system inside lithium-ion batteries experiences a reduction in activity, significantly increasing charge transfer impedance (Rct).

Smartphone users, for the most part, only need to charge their phones once a day. However, for users who engage in gaming or heavy usage, there may be instances of multiple charges during a single day, but this is not the norm.

Power bank users, on the other hand, have larger battery capacities and lower usage frequencies (they only use power banks when their phone’s battery is low). Consequently, the frequency of charging (i.e., one cycle of the lithium-ion battery) is the lowest among these three scenarios.

Therefore, in practical applications, smartphone batteries may remain healthy for only about three years. Even if you consistently use a power bank to charge your smartphone, the power bank’s larger battery capacity can extend its lifespan beyond that of a smartphone.

Understanding Lithium-Ion Battery Lifespan: Why Smartphones Age Faster Than Power Banks

Currently, both mobile phones and power banks use similar lithium compound batteries, and these batteries have a limited lifespan.

We typically measure the lifespan of lithium-ion batteries not in years but by the number of “full charge and discharge cycles.” Generally, these batteries have a lifespan of around 500 to 600 cycles. However, if we must use a time-based measurement, it’s usually around 3 to 4 years. Nowadays, many smartphones even come with a promise of maintaining battery capacity at no less than 80-85% after 4 years of use.

It’s essential to note that the degradation of lithium-ion batteries is gradual and not immediate. Their performance gradually decreases with increasing usage years. Therefore, some lithium-ion batteries can still function properly even after ten years of use, albeit with reduced battery life. Apart from diminished battery life, they can continue to serve their purpose.

The reason behind the lifespan of lithium-ion batteries is closely tied to their internal structure.

In simple terms, a lithium-ion battery consists of lithium-ion material as the battery core, with positive and negative electrodes separated by an electrolyte. When we charge the battery, lithium ions within the battery undergo an intercalation process. When the battery is used to power other devices, these lithium ions, which have undergone the intercalation process, undergo de-intercalation, releasing electrons to supply power to the device. As the battery’s usage years increase, the number of lithium ions gradually decreases, with some ions losing their effectiveness. Consequently, the battery’s lifespan decreases, leading to reduced battery capacity, or in other words, reduced battery life.

The reason for using “full charge and discharge cycles” as a measure is that one complete charge-discharge cycle consumes the lithium ions' activity.

With this understanding, we can intuitively comprehend why smartphone batteries decline after a few years, while the lifespan of power bank batteries is much longer.

For smartphones, our usage frequency is exceedingly high. Most modern smartphones have a battery life of about one day under full charge. This means that we charge and discharge our phones daily. Although we rarely achieve a 0% to 100% charge or a 100% to 0% discharge, frequent charging and discharging continually deplete the lithium ions' activity. Over time, this leads to a gradual reduction in the smartphone battery’s capacity. When the battery’s lifespan decreases significantly, its battery life diminishes, and eventually, it reaches the end of its life cycle.

In contrast, power banks have a much lower usage frequency compared to smartphones. Especially when used for personal purposes, power banks may be used only a few times throughout the year. Thus, they naturally have a longer lifespan. For infrequently used power banks, as long as they undergo periodic charging and discharging when not in use, they can last for seven, eight, or even ten years.

However, shared power banks that are heavily used by many people may not last as long.

Why Smartphone Batteries Age Faster Than Power Banks: Factors to Consider

In the past, when mobile phone batteries had smaller capacities and limited battery life, using a power bank was a common practice. However, with the introduction of new smartphones with large battery capacities, such as the Vivo S18e with a 4800mAh battery and 80W fast charging, the landscape has changed. These advancements not only improved the quality of smartphone batteries, making them more durable and long-lasting but also increased their charge-discharge cycles, significantly enhancing battery life. With such improvements, one can easily go a day without needing to charge their phone, making power banks less necessary.

In contrast, the frequency of using power banks has decreased. People typically use power banks when traveling long distances by train, embarking on journeys lasting over 8 hours, or when concerned about the unavailability of charging facilities during their trip. Consequently, power bank usage is relatively infrequent.

So, why do smartphone batteries deteriorate after a few years while power banks don’t seem to face similar issues? There are three primary factors to consider.

1. Different Usage Scenarios

Smartphone batteries and power banks, despite both being battery products, have significant differences in usage scenarios and design functionality.

Smartphone batteries are an integral part of mobile phones and are responsible for providing the necessary power for various daily activities, such as calling, texting, taking photos, and gaming. These activities consume a significant amount of battery power.

In contrast, power banks serve as temporary energy storage devices designed to provide additional power when our devices, like smartphones, run low on battery. Power banks typically have larger battery capacities and longer battery life due to their lower usage frequency. Consequently, power banks tend to have longer lifespans.

In essence, almost everyone has a smartphone, but not everyone owns a power bank.

2. Different Usage Habits

The lifespan of smartphone batteries is influenced by various factors, including usage frequency, charging habits, and battery quality. Frequent charging and discharging, as well as using subpar chargers and cables, can lead to a shortened battery lifespan. Due to higher personal usage habits and frequencies, smartphone batteries naturally have lower durability compared to power banks.

In contrast, power banks have lower usage frequencies and do not require frequent recharging like smartphone batteries. When designing power banks, portability and charging speed are prioritized, allowing them to quickly provide additional power when needed to meet temporary requirements.

3. Batteries Are Just a Small Part of a Phone

When considering smartphones in the thousand-dollar range, the battery is just one component of the device. When buying a smartphone, consumers evaluate various factors, including battery capacity, performance, camera capabilities, and more. Power banks, on the other hand, primarily serve the function of providing power to smartphones, focusing on a single purpose. Therefore, comparing the battery of a thousand-dollar smartphone to a standalone power bank may not be a fair comparison.

Of course, to protect the lifespan of smartphone batteries, it’s essential to develop good charging habits. Avoid prolonged charging, use compatible chargers, regularly clear background processes, and close unnecessary applications. These practices can effectively extend the lifespan of smartphone batteries.

Why Smartphone Batteries Deteriorate Faster Than Power Banks: Factors to Consider

The core factors contributing to the difference in lifespan between smartphone batteries and power banks are twofold:

1. Smartphone Battery Usage Frequency and Absolute Capacity Are Much Higher Than Power Banks, Making It Easier to Reach the “Dangerous Capacity” Threshold of 80%.

2. People Have a Lower Tolerance Threshold for Battery Drain in Smartphones, Leading to “Low Battery Anxiety” and Frequent Upgrades.

In reality, the durability of smartphone batteries is longer than many people might think. According to official statements, after 500 charge cycles, a smartphone battery may lose 10% of its capacity. After 1000 cycles, it may lose another 10%, resulting in an overall health of around 80% after 1000 charge cycles. It’s important to note that a charge cycle refers to the process where the smartphone battery goes from a full charge to its lowest capacity and then back to a full charge.

Smartphones are essential daily digital devices, experiencing the highest usage and frequency. For most people, who often work 9 am to 9 pm, their phones are rarely turned off. Based on my own usage of an iPhone 15 Pro, the daily average battery consumption over the last 10 days is roughly equivalent to one charge cycle. This means that after using it for 2 years, the smartphone battery’s health may be around 85%, and it might take around 3 years to drop to 80%. Interestingly, that’s about the same frequency at which I upgrade my phone.

However, my usage frequency is relatively low compared to those who use their smartphones heavily, play games, or watch videos regularly. For such heavy smartphone users, their battery health might drop to 80% in about 2 years.

Power banks, on the other hand, are less likely to face these issues.

In my possession, I have a total of three power banks. One was purchased 2 years ago, another 5 years ago, and one whose purchase date I’ve forgotten. I haven’t thought about replacing any of them because they are rarely used. On average, I don’t need to use a power bank even once a week, and their usage is mostly for emergencies. For instance, when accompanying my wife for shopping and realizing I forgot to charge my phone beforehand, or when I forget my phone charger while traveling. However, in most cases, using a power bank is unnecessary. With MagSafe wireless charging at home and in the office, along with a USB-C cable to connect to my MacBook while traveling, my iPhone 15 Pro’s battery lasts a whole day without any issues. Therefore, the power consumption of power banks is much lower compared to smartphone lithium-ion batteries.

Another point to consider is the total capacity. Smartphone lithium-ion batteries generally have capacities ranging from 2500mAh to 5000mAh, while power banks typically start at capacities of 10,000mAh or higher. This means that the initial capacity of power banks is 2 to 4 times that of smartphone batteries. In terms of equivalent power consumption, power banks naturally have fewer theoretical charge cycles than smartphones. When combined with lower usage frequency, power banks appear to be more durable.

Another aspect to consider is users' anxiety about low smartphone battery levels and battery health.

Even with an 80% battery health, using a smartphone can often feel restricting. Firstly, because the absolute capacity is lower, resulting in shorter usage durations. Secondly, certain usage scenarios are power-hungry, such as gaming on a hot day, maxing out screen brightness for HD videos, or using USB connections for high-power audio devices while listening to music. In such situations, the battery can drop by one or two bars in just 1-2 minutes, which is intolerable for most users.

Even though modern large-screen smartphones come with higher-capacity batteries, the increase in power consumption due to upgraded hardware components like screens, processors, and cameras cannot be ignored. Many high-capacity batteries still require 2-3 charges a day in high-power usage scenarios. While fast charging can alleviate battery anxiety, it also accelerates battery degradation and shortens the upgrade cycle.

Once the battery health drops to 80%, with the more frequent charging, users face a choice: either replace the battery or upgrade the entire phone. In most cases, the latter is the preferred choice.

Why Smartphone Batteries Deteriorate Faster Than Power Banks: Understanding the Fundamental Differences

The most fundamental reason lies in the difference in work conditions!

Firstly, it’s important to clarify that both the lithium-polymer batteries used in smartphones and the 18650 specification lithium-ion batteries commonly found in power banks belong to the family of lithium-ion batteries. They share more similarities than differences and are both subject to limitations in terms of charge cycles.

So why do smartphone batteries tend to appear less durable, with issues like declining health and reduced charge capacity occurring after just 1 or 2 years, while power banks rarely face such problems?

The working principle of lithium-ion batteries involves the movement of lithium ions between the positive and negative electrodes and the electrolyte in the form of intercalation and deintercalation during the charge and discharge processes. In simpler terms, it’s the back-and-forth motion of lithium ions between the positive and negative electrodes.

However, as the number of charge and discharge cycles increases, a passivation layer known as the SEI (Solid Electrolyte Interphase) film gradually forms around the negative electrode of the battery. This film inhibits the movement of lithium ions within the electrolyte, leading to increased energy loss and ultimately causing a decline in battery capacity.

In general, the lifespan of lithium-ion batteries is approximately within 300 to 500 full charge and discharge cycles. Beyond this cycle count, batteries usually exhibit noticeable capacity degradation.

So, besides reducing the actual energy provided by the battery, a more critical issue is that as the battery’s capacity decreases, the voltage output to the boost circuit also decreases, resulting in increased pressure on the boost circuit.

Especially with the current trend of smartphones becoming more powerful, the corresponding increase in power consumption is substantial. The chart below shows the power consumption of some mainstream smartphone CPUs, highlighting significant differences in power usage between high and low-end configurations. The Qualcomm Snapdragon Gen1, for example, consumes as much as 11.1W, and this is just considering the CPU alone without factoring in other components like the motherboard, screen, and more.

This explains why smartphone battery capacities have increased significantly, but actual screen-on time hasn’t seen a proportional increase. The higher power consumption inherently means faster battery depletion, resulting in more frequent charge and discharge cycles. Personally, whether it’s an Android or iPhone, if I don’t manage my usage well, I find myself needing to charge 2 or even 3 times a day.

In contrast, today’s power banks, also known as “mobile power sources,” typically come with capacities ranging from 10,000mAh to 20,000mAh. Conservatively estimating, they can provide at least two full charges for mainstream smartphones today.

This means your smartphone may undergo 1 to 2 cycles of its lifespan daily, while a power bank might only go through 0.5 to 1 cycle at most. Given the same 500 cycles, who do you think will wear out faster? The answer is quite clear!

Furthermore, the working environment for power banks is relatively comfortable compared to smartphones. As long as they are from reputable manufacturers, their output power is generally tied to internal temperature control. If the temperature is too high, the output automatically reduces, ensuring safety. While smartphones also have temperature control, it carries less weight, especially when people enjoy gaming or watching videos while charging, which are high-power operations. The additional heat generated during phone charging compounds the environment’s harshness. High temperatures are also detrimental to the lifespan of lithium-ion batteries, accelerating aging and reducing their lifespan.

PS: Power bank batteries can also experience a decrease in “health,” but relatively fewer people pay attention to it compared to smartphones. Additionally, power banks usually come into play only when our smartphones are running low on battery. Unlike smartphones, which need to be on standby 24/7, even if the battery capacity declines, it won’t be as noticeable.

Even if we consider the scenario of replacing a power bank, it’s relatively easy on the wallet, costing just a few tens to a couple of hundred dollars at most. In contrast, replacing a smartphone battery, not to mention the cost, can be a hassle. From a psychological perspective, it’s easier for people to remember that smartphone batteries are prone to problems while power bank batteries are not – even if that’s not entirely accurate.

Why Smartphone Batteries Deteriorate Faster Than Power Banks: Understanding the Fundamental Differences

Firstly, your conclusion is incorrect.

First, if you’ve ever encountered a swollen power bank… I’ve had several swollen power banks that I had to dispose of because they were out of warranty, had no repair value, and posed safety risks. So, doesn’t a swollen power bank count as a problem? I think it certainly does.

Now that we’ve established this fundamental fact, let’s understand why there’s an intuitive perception that smartphone batteries become unusable after a few years. Firstly, the usage patterns of smartphones and power banks are different. Smartphones have gradually become one of the essential electronic devices for everyone. Whether it’s making payments, ordering food, or just stepping out of the house, smartphones are indispensable. Consider a few years back when you didn’t have a smartphone. How would you prove your identity or perform various tasks? Therefore, the usage frequency of smartphones today is extremely high.

Today’s smartphones also tend to be high-performance devices with better screens. Most mid-range and above smartphones now come with OLED displays, which offer excellent visual quality but consume more power. It’s common to hear people say they charge their smartphones daily, and for some users with high usage, like gaming or video streaming, even multiple charges a day are necessary.

Charging your phone daily means the battery goes from 100% to 0% and then back to 100%. Even if it’s not that extreme and you go from 80% to 20% and back to 80%, the essence is the same. One cycle per day means 1,000 cycles in 3 years, which will cause wear and tear on even the best batteries.

However, power banks don’t operate this way. Firstly, power banks are not the primary method for charging; they are used in emergencies when your phone is running out of battery or when you can’t access a wall socket while on the move. Additionally, because power banks are meant for emergencies, many people, or at least I have this habit, carry two or more power banks. When one is running low on power, you charge it, and when another one has more charge, you switch to it. After all, power banks are for emergencies; it would be comical if your power bank ran out of battery when your phone was already dead.

Another point to consider is that most people choose power banks with higher capacity, hoping that one full charge from the power bank can completely charge their smartphones. In other words, when most people charge their smartphones to one bar using a power bank, the power bank still has some charge left. Even with a 1:1 charge-discharge ratio, power banks have fewer cycles than smartphones. So, most of the time, the cycle count of power banks is significantly lower than that of smartphones, naturally giving the impression of durability. If you don’t believe it, try discharging and charging a power bank every day; it may not outlast a smartphone.

Other factors, such as high integration in smartphones, heating due to simultaneous charging and usage, and excessive charging power, also affect the lifespan of smartphone batteries to some extent. Power banks are generally less affected by these factors. Taking all these factors into account, it becomes evident why smartphone batteries seem to deteriorate after a few years.

The Fundamental Difference in the Lifespan of Smartphone Batteries vs. Power Banks

Having a thousand smartphones doesn’t mean you bought a thousand batteries; it’s a combination of components such as the motherboard, CPU, GPU, display screen, camera modules, and more. On the other hand, power banks, costing a few hundred dollars, are essentially just a rechargeable battery.

Comparing the two based on price doesn’t make much sense.

The primary difference between the lifespan of smartphone batteries and power banks lies in their usage frequency.

Both smartphone batteries and power banks are typically Lithium Polymer (LiPo) batteries, and their working principle is something we learned in middle school – they are devices that convert chemical energy into electrical energy. They consist of a positive electrode, negative electrode, and an electrolyte.

The positive and negative electrodes are separated by the electrolyte, which enables a chemical reaction between the positive and negative electrodes, resulting in the generation of electrical energy.

Currently, battery lifespans are quite high. New smartphones on the market today can endure around 1600 charge and discharge cycles. Assuming normal usage with a full charge and discharge once a day, the battery’s actual capacity will be about 80% of the initial capacity after three to four years.

The charge and discharge cycle count refers to a full charge and discharge. For example, if you use 60% of the battery on the first day, then charge it fully, and later use 40%, this counts as one charging cycle.

According to official explanations, theoretical charge cycle count means that after reaching a certain number of cycles, the battery’s actual capacity will be less than or equal to 80%, indicating that the battery is in an unhealthy state and its charge cycle count starts increasing. At this point, you might consider replacing the battery, but it doesn’t mean it’s completely unusable.

Furthermore, most smartphones have a built-in battery health monitoring feature. In my VIVO smartphone, for instance, there’s a battery maximum capacity indicator in the battery settings, as shown in the image I captured below. After over a year of use, my battery’s maximum capacity is still at 90%.

Of course, these figures are theoretical values, meaning they are the maximum theoretical cycle counts promoted by the manufacturers. These theoretical cycle counts are achieved under specific conditions, including particular environments, temperatures, humidity levels, specific usage patterns, and charging/discharging methods that normal users can hardly meet.

Returning to the main question of why smartphone batteries deteriorate after a few years while power banks don’t face similar issues, the fundamental reason lies in the difference in usage frequency.

Typical smartphone batteries have a capacity of around 5000mAh, while power banks start at a minimum of 10,000mAh and can even reach 20,000mAh or 50,000mAh. Even an average 10,000mAh power bank can charge a smartphone fully twice.

If every time you drain your smartphone, you use a power bank to recharge it, a 10,000mAh power bank will complete one charge and discharge cycle while your smartphone will complete two. If the number of charge and discharge cycles for both the smartphone battery and power bank is the same, the power bank’s durability is at least double that of the smartphone.

Moreover, most people primarily use the original charger to charge their smartphones regularly, while power banks are only occasionally used as a backup. The power bank might be charged once a week or even less frequently, significantly reducing the usage frequency. Comparing the lifespans of the two under such circumstances makes them incomparable.