I am a new iPad 2 user and have a naive question. Normally, I charge my iPad once a couple of days and use it while it is discharging. Then, I charge it again once the charging levels have reached 10-15%. Is this mode of usage optimal for the longevity of the battery? Or should I keep the battery charging while I'm using the iPad? I do not have a docking station (since I'd opted for a smart cover instead) but I can still keep it connected to the power outlet on my office desk. On a related note, how long does the iPad battery keep giving optimal performance?