Why is my ipod shutting down then turning back on??

So my iphone 4s with IOS7 was in recovery mode when i got it off my sister, After i restored it(After restoring failed 5 times before), i would try and charge it but the apple logo would come one and then turn off. This keept happeneing the time between getting longer and longer. Until now i can actually use it, (I put it on charge and turned it off.) So now this morning its is on 91% but after a minute it will just **** down then turn on again. What the **** is it doing???