Do you have alarms set? Alarms work (at least on the phone) even when the iPad(iPhone) is turned off. So it could be listening or checking the time. Not sure how it works.
I pad is great things in this busy life. There are many type of ipad available in markets. As well as many useful parts in this ipad. Battery is most important part in i pad. Generally I pad battery use to around 10 hours.