I'm using the iPad 2 alot more now and want to know if leaving it on the charger will do it any harm for hours on end.
continously charging will reduce the quality of your battery faster its better to unplug it when u reach 100% and drain it to ~10% before plugging it back in
Technically the iPad/iPhone batteries are made to withstand an unlimited number of partial charges, without lowering the battery lifespan. In practice though, the effect is still there but it is greatly reduced. Yes you'd be safer with plugging it in once the battery is low, but keeping it on charge won't be that bad for it. As long as you have a full drain followed by a full charge about every two weeks.
My opinion is it won't do it any harm I leave my ipod docked most of the time and it hasn't seemed to have any effect apart from being conveniently charged when I actually want it. Pretty sure that when they get to 100% they have circuitry to stop them overcharging.
For the batteries in these devices it is not good for them to be at 0% or 100% for extended periods. Other than that it really doesn't matter, if it is at 75% it's ok to charge if it is 20% it's ok, if it is at 99% it's ok. It is not good to leave them drained or constantly charged. I researched this last week matter of fact. Apple does recommend for you to take it down to <10% and back up to 100% once a month, but that is so the charge percentage is put back on track it has very little to do with the health of the battery.
