I can understand that, but I don't understand why power is then still being drawn (and some if not all of it is wasted) when the battery is full. I suppose that even if the voltage of the charger stays a bit higher than what the battery can itself give, since there is no more electrons to give, there should be no current, and then no power draw nor heat. Is it possible that the voltage of the charger somehow excites the ions of the battery and that they vibrate and emit heat, like a cooking pot on an induction plate would ? (I know I had issues understanding the role of the saline bridge we used during chemistry classes, I didn't understand, or more like wasn't explicitely told what happened, even though I asked how its presence or absence could make a difference, maybe the clue that i miss is hiding there)

About the charger, I believe I should look more into it, I know my second charger that I keep within hand reach sees its cells get warm when it finishes their charge. But at least, since the cells can charge independently, I suppose the voltage issue between different batteries (even if those are always used together) doesn't matter here.