Compared to iPhone, iPad has a HUGE battery duration. I have to recharge my iPhone once per day, if I make sort of heavy use (I mean, check e-mail at least 15 times, read/browse 30-60 minutes, use gps or maps for a total of 30-60 minutes). And in general this drains the battery in less than the whole day (I have a Mophie case with extended battery).
The same usage but with iPad: at the end of the day I have 70% battery left.