My extended battery takes about 4 hours to charge when the phone is on while it is charging (even if I'm not using it). If I turn the phone off, it takes less than half of that time to charge. It's not so bad turning off my phone to charge while I'm sleeping... IF the phone could make it through the whole day without another charge. Unfortunately, I'm only getting 8-10 hours of battery life WITH the extended battery, so I have to charge half way through the day. I don't like having to turn off the phone during the day, but I don't really have a choice if I want to keep it charged.
This battery life / charing issue is my achilles heel with this phone: I'm loving just about everything else on the phone, but I really thought I'd be okay with the extended battery. But so far, I'm extremely disappointed (and I'm not even on 4G yet).