This is a chemistry question, batteries work on chemical energies, without a long winded chemical explanation it is ALWAYS better to not leave them plugged in the entire time, and it is ALWAYS better to let them deplete completely before recharging. However the chemical reaction will ALWAYS degrade over time, those two things only make it last longer, it depends ont he reaction but you could literally extend the life of a battery a thousand times if you follow this principle.
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