oh thats a silly method. The option should be "slow charge during sleep mode" and how far down the battery is allowed to discharge (although I admit, that maybe the 80% charge is a full charge and it really doesnt allow it to discharge past 20%)

Slow charging reduces wear on the battery, and you can get a full charge by the morning. My assumption here is that if you are charging during the day, you want it to be faster because you need it.

https://www.batterypowertips.com/how-fast-can-li-on-batteries-be-charged/

Its depth of discharge that is a battery killer. You can fully charge a battery without extra heat, you just charge it slower and longer.

https://ecosoch.com/lithium-ion/