usually happens to old IB and EP's ) when they have been sitting around for longer than a few months. they like to be used weekly to keep IR low.
or cheap shit ebay chines batteries. i bought 8 aa chinese batt for my tx from ebay. soldered them together they peaked at 15+V, when they should peak at 1.55v each or 12.v for the entire pack.
RIP Kanye West ..... Mom