How Long Do Lithium Batteries Really Last? The Truth Revealed

Lithium-ion batteries are a type of battery that uses lithium metal or lithium alloys as the negative electrode material and a non-aqueous electrolyte solution. The earliest lithium metal battery was proposed and studied by Gilbert N. Lewis in 1912. In the 1970s, M.S. Whittingham proposed and began researching lithium-ion batteries. Due to the highly reactive chemical properties of lithium metal, its processing, storage, and use require very strict environmental controls. Therefore, lithium-ion batteries were not widely used for a long time. With the development of science and technology, lithium-ion batteries have now become mainstream.

Lithium batteries can be broadly classified into two categories: lithium metal batteries and lithium-ion batteries. Lithium-ion batteries do not contain metallic lithium and are rechargeable. The fifth generation of rechargeable batteries, lithium metal batteries, was developed in 1996. They offer superior safety, specific capacity, self-discharge rate, and price-performance ratio compared to lithium-ion batteries. Due to their high technological requirements, only companies in a few countries currently produce lithium metal batteries.

Lithium-ion batteries can only be charged and discharged 500 times?

Most consumers have probably heard that lithium batteries have a lifespan of "500 cycles," meaning 500 charge-discharge cycles. Beyond that, the battery is considered "dead." Many people try to extend battery life by charging the battery only when it is completely depleted. But does this really extend battery life?

❌ The answer is no. The lifespan of a lithium battery is "500 times," which does not refer to the number of times it is charged, but rather to one charge-discharge cycle.

A charging cycle means the process of a battery going from fully charged to empty and then back to fully charged, which is not the same as charging once. For example, if a lithium battery is used up to half its capacity on the first day and then fully charged, and the same thing is done on the second day, this only counts as one charging cycle, not two. Therefore, it usually takes several charging cycles to complete one cycle. Each time a charging cycle is completed, the battery capacity decreases slightly. However, this decrease is very small; high-quality batteries retain about 80% of their original capacity after many charging cycles, and many lithium-ion battery-powered products still function normally after two or three years. Of course, lithium-ion batteries still need to be replaced when they reach the end of their lifespan.

The so-called 500 cycles refers to the manufacturer achieving approximately 625 rechargeable cycles at a constant depth of discharge (e.g., 80%), reaching 500 charging cycles. (80% * 625 = 500) (ignoring factors such as the reduction in lithium battery capacity).

However, due to various factors in real life, especially the fact that the depth of discharge during charging is not constant, "500 charging cycles" can only be used as a reference for battery life.

The correct statement is: the lifespan of a lithium battery is related to the number of completed charging cycles, but not directly related to the number of charges.

To put it simply, for example, if a lithium battery is used only half its capacity on the first day and then fully charged, and the same thing is done on the second day, this only counts as one charging cycle, not two. Therefore, it usually takes several charging cycles to complete one cycle. Each time a charging cycle is completed, the battery capacity decreases slightly. However, the decrease is very small; high-quality batteries will still retain 80% of their original capacity after many charging cycles. This is why many lithium-ion battery-powered products still function normally after two or three years. Of course, lithium-ion batteries eventually need to be replaced when their lifespan is reached.

The lifespan of a lithium battery is generally 300-500 charging cycles. Assuming a single full discharge provides Q units of electricity, and disregarding the reduction in capacity after each charging cycle, a lithium battery can provide or replenish a total of 300Q-500Q units of electricity over its lifespan. Therefore, if you charge after using half the battery capacity each time, it can be charged 600-1000 times; if you charge after using one-third of the battery capacity each time, it can be charged 900-1500 times. And so on. If you charge randomly, the number of charges is uncertain. In short, regardless of how you charge, the total amount of electricity replenished is constant at 300Q-500Q. Therefore, we can also understand it this way: the lifespan of a lithium battery is related to the total amount of electricity it can be charged, not the number of charging cycles. Deep discharge/deep charge and shallow discharge/shallow charge have little difference in their impact on the lifespan of a lithium battery.

In fact, shallow discharge and shallow charge are more beneficial for lithium batteries. Deep discharge and deep charge are only necessary when the product's power module is calibrating the lithium battery. Therefore, products powered by lithium batteries do not need to be too particular about the process; convenience should be the priority. Charge them whenever you want without worrying about affecting their lifespan.

If lithium batteries are used in environments exceeding the specified operating temperature (above 35°C), the battery capacity will continuously decrease, meaning the battery's power supply time will not be as long as usual. Charging devices at such temperatures will cause even greater damage to the battery. Even storing batteries in relatively hot environments will inevitably cause some damage to their quality. Therefore, maintaining a suitable operating temperature is a good way to extend the lifespan of lithium batteries.

If you use lithium batteries in low-temperature environments, i.e., below 4°C, you will also find that the battery life is reduced, and some original lithium batteries in mobile phones may not even charge in low-temperature environments. But don't worry too much, this is only a temporary situation. Unlike use in high-temperature environments, once the temperature rises, the molecules in the battery are heated and immediately recover their previous capacity.

To maximize the performance of a lithium-ion battery, it needs to be used frequently to keep the electrons inside constantly flowing. If you don't use your lithium battery often, remember to complete a full charging cycle each month and perform a charge calibration, i.e., a deep discharge followed by a deep charge.

The proper term is "charge-discharge cycle," not "number of charges." A cycle refers to the time a battery goes from fully charged to completely depleted. If your battery is fully charged, used up to one-tenth of its capacity, and then fully charged again, that's one-tenth of a cycle. You need to charge and discharge it 10 times to complete one cycle. Similarly, if you start from a full charge, use up half the capacity, fully charge it, then use it up again to half the capacity, and then fully charge it again, that's also one cycle—you've charged it twice. Therefore, a cycle depends solely on "the total amount of electricity discharged from the battery," and has no direct relation to "the number of charges."

Furthermore, this nominal number of charge-discharge cycles doesn't mean the battery is unusable once it's exhausted. Rather, it means that after this many cycles, the battery's ability to store electrical energy will decrease to a certain level.

For example, a certain lithium battery has a nominal charge-discharge cycle life of "no less than 60% of its nominal capacity after 500 cycles".

In other words, after 500 cycles, this battery can only hold about 60% of the capacity it had when it was new. Its performance has decreased to a certain extent. That's the gist of it.

Lithium batteries do not have a fixed limit on the number of charging cycles. Batteries from reputable manufacturers can generally withstand at least 500 charge-discharge cycles while maintaining more than 80% of their initial capacity, meaning they can last for two years on a single charge. Typically, mobile phone batteries will experience significant degradation in battery life after 1000 charge cycles.

Mobile phone battery maintenance methods:

1. Use the battery only when it is fully charged each time to reduce the number of charging cycles and extend battery life.
2. You don't need to fully discharge the battery; it usually needs to be charged when the charge level drops below 10%.
3. Use the original charger to charge; do not use a universal charger.
4. Do not use your phone while it is charging.
5. Do not overcharge; stop charging once the battery is fully charged.

Yes, according to experimental results, the lifespan of lithium batteries decreases with increasing number of charging cycles. Generally, lithium batteries can only withstand 2000-3000 charging cycles.

Cycling refers to usage. We are using batteries and are concerned with the duration of use. To measure the performance of a rechargeable battery, the definition of cycle life is established. Actual user experiences vary greatly, and tests under different conditions are not comparable. To make comparisons, the definition of cycle life must be standardized.

The national standard specifies the following test conditions and requirements for the cycle life of lithium batteries: Under an ambient temperature of 20℃±5℃, charge at 1C. When the battery terminal voltage reaches the charging limit voltage of 4.2V, switch to constant voltage charging until the charging current is less than or equal to 1/20C. Stop charging and let it rest for 0.5h~1h. Then discharge at 1C current to the termination voltage of 2.75V. After the discharge is completed, let it rest for 0.5h~1h before starting the next charge-discharge cycle. The cycle life is considered to have ended when two consecutive discharge times are less than 36min. The number of cycles must be greater than 300.

Explanation of the national standard:

1. This definition specifies that cycle life testing is performed using a deep charge-deep discharge method ;
2. The regulations stipulate that, according to this model, the cycle life of lithium batteries should still retain more than 60% of their capacity after ≥300 cycles .

However, different cycling regimes yield drastically different cycle counts. For example, keeping all other conditions unchanged, simply changing the constant voltage from 4.2V to 4.1V for the same battery model during cycle life testing means the battery is no longer being deep-charged, and the final test results show a nearly 60% increase in cycle life. Therefore, if the cutoff voltage is increased to 3.9V, the cycle count should increase several times over.

The claim that each charge-discharge cycle reduces battery life is important to understand. A lithium battery charging cycle is defined as the process of a lithium battery going from fully charged to completely empty and then fully charged again. This is not the same as charging once. Furthermore, when discussing cycle count, the conditions under which the cycle is performed must be considered. Discussing cycle count without considering these conditions is meaningless, as cycle count is a means of assessing battery life, not the end goal!