I have a new iPad 3 that tends to power itself off after a while if it's not connected to a charger. Not just turn off the screen and lock it, actually power off so I have to hit the power button to turn it on again and wait for it to start up. The battery isn't drained (usually it's at 100%-99% when it's done this). I've erased it and re-set it up as new, but no change. 6.0.1 iOS. Any thoughts?