sony phones are chronic for this kinda thing , bought her a sony phone for christmas gone , was sent for first repair within 3 months , covered under manufactures warrenty thankfully , it was away for a month , had it back 3 weeks or so and started doing the same trick again , brought it to a local guy who updated some stuff on it and advised her never to let the battery level go below 20% as there is an unfixable flaw that wont allow the phone to charge if drops below this , something in the software apparently ,