Recent 9.2.1 update led to battery now discharging overnight. Apple retail clerks no clue....thoughts?

Our Ipad (2nd gen) has been working perfectly. We took the 9.2.1 upgrade. Now it discharges overnight, regardless of what apps we disable, features, etc. We've tried the discharge for 24 hrs trick; that doesn't work. The store clerks gave us pat answers, so is there any way to go backwards to the prior OS? (otherwise we have to spend hundreds for physical repair or I guess buy a new one)