@Rickbflony You should charge your phone no more than 90% and let it discharge no more than 20% for extended battery life.
This is how electric cars make the battery last so long.
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@Longbowgun @Rickbflony This varies with the type of battery but the principle does apply to all (I think) modern batteries.
Cold also helps. If you want to keep an old phone in good operation when not in use keep it in the refrigerator.