Lithium-ion batteries lose a little capacity every time they are charged and discharged. Generally, the current cycle number of lithium batteries is 1500-2000 times. The picture below is mentioned in a literature. Picture a is the voltage curve at different aging stages , and picture b is the available capacity, also called the health state. 1 means new High quality laptop battery, 0 means completely scrapped. In fact,
the bulk is almost unusable after 80% SOH is used (electric vehicle battery scrapping indicator). Because with aging , the battery capacity decreases and the internal resistance increases. The former results in insufficient available power, and the user experience is that it needs to be charged soon, and it will not last long after charging once. The latter causes the battery to heat up during use.
So can this aging be avoided? the answer is negative. In other words, no matter what brand of mobile phone battery or laptop battery, there is aging and capacity decline. This decline rate is related to usage. This is an empirical formula:
The loss of capacity is related to temperature T and Ah (ampere-hour throughput). The higher the temperature, the faster the aging. The more accumulated charge and discharge of electricity experienced, the greater the aging.
As the battery ages, the internal resistance becomes larger and larger, and it gets hotter and hotter, and the heat accelerates aging, which is a vicious cycle.
Regardless of the form, they are all connected in series (rarely in parallel)
Since they are connected in series, there are inevitably inconsistencies in the laptop batteries including inconsistencies in internal resistance, open circuit voltage and capacity. When they first leave the factory, they are all screened and the inconsistencies are not obvious. But after a long time of use, there will be a wooden barrel effect.
There is always a shortcoming of a battery that restricts other batteries. For example, if one battery has a low capacity and disappears after being left for a while, then other batteries are useless if they have power. Lithium batteries are not allowed to be over -discharged; if there is a battery with the highest capacity, it will be fully charged after a while. , then other batteries are not fully charged and cannot continue to be charged. Lithium batteries are not allowed to be overcharged. Therefore, the battery pack determines the amount of power that can be used by these two battery cells.
Returning to the topic of laptop batteries, there is a possibility that the inconsistency of the battery pack has reduced the available power. It will be full after charging and empty after a while after discharging. In this case, the available service life of the battery pack is much lower than that of a single laptop batteries ,battery pack.