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Do batteries really lose the ability to hold a charge if they are plugged in often/on a schedule?(r/askscience)
For Li-ion cells, there are two things:
- Cycle life
- Calendar life
Cycle life is indeed affected by the depth of discharge, but also by other factors such as temperature and peak current.
Calendar life is limited regardless of whether the cell is used or not. It is worst (shortest life) at high state of charge (100 % full).
There are two mechanisms that reduce the life of a cell:
- decrease in capacity
- increase in internal resistance
The decrease in capacity is real, but not the whole story.
The increase in resistance is often the real reason that a cell reaches its end of life, even if the capacity is still acceptable. That is because resistance results in voltage sags under load. With higher resistance, the sag is deeper, until it reaches the point that the device that is being powered can no longer operate. What appears as a reduced capacity, is actually increased resistance.