i too would experience the same fault with my iphone 5 where it constantly rebooted on end and it came to a point where it wouldn't work off charge , i researched all possible solutions regarding hard rebooting , deleting apps , updating , and resetting to factory settings but it all didn't work , the problem was a simple hardware fault from dropping my phone , all that needed to be done was unscrew and open up my iphone and just remove the battery and reconnect it , the only problem was the connection and now it's working perfectly , instead of wasting money at phone shops , simply open your phone at home and make sure your battery is connected properly.