Thermal degradation & regulation can be flaky in cheaper stuff, which is part of what the slowdown is about avoiding (and also stuff on a purely electrical chemistry level).
Some higher power devices instead have active cooling with fans, radiators & so on.
> what you should avoid is fully discharging
Yeah, lithium chemistries don't like that.
(It's actually helpful if not outright necessary for NiMH.)
> having it permanently sitting at 100% with the charger plugged in.
I noticed (and use) that feature to keep it at maximum 80% on those devices that have it.
Trickle-charging is supposedly not ideal either, but considerably better than overcharging.
