My iPad rests at night by the side of my bed so that, immediately on awakening, I can get my 'fix' on Kitz forums and other global newsworthy events. I've kind of got used to the fact, if the battery is low at bedtime, even in sleep mode, it'll probably be nearly useless by breakfast time.
Surprise them to find, after being away on hols in the west contry for four days last week, iPad left behind after several hours use, not on charge, battery was still 70% when I awoke the device. One possible difference was, house being empty I'd switched off the router and modem, thus preventing any internet chatter.