The lithium-ion battery works on ion movement between the positive and negative electrodes. In theory such a mechanism should work forever, but cycling, elevated temperature and aging decrease the performance over time. In a conservative approach, the lifetime of Lithium Ion batteries is specified as follows: after 400 - 500 discharge/charge life cycles, the battery capacity will be as low as 50% of its original capacity.
Similar to a mechanical device that wears out faster with heavy use, the depth of discharge (DoD) determines the cycle count of the battery. The smaller the discharge (low DoD), the longer the battery will last. If at all possible, avoid full discharges and charge the battery more often between uses. Partial discharge on Lithium Ion is fine. There is no memory and the battery does not need periodic full discharge cycles to prolong life.
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