We have used our IPads plugged in with zero problems. As for extending the battery life, I wouldn't completely deplete the battery and leave it sitting for any length of time. My rule is try and plug it in no lower than 10% but most of the time I recharge at 20%. As for cords, I'm not sure to be honest. The iPad has a really decent battery life unless you spend a lot of time watching movies. Just misc dealing starting in the early morning till bed time still has me around 20% -/+. Watching a full length movie can zap 30-50%. So you shouldn't have to have it plugged in all the time.
Ps: adjusting the scream brightness to full or max brightness will use more power. I like to keep mine at around 50-80%...cutting back to extend battery life when it's low.
