Phone shuts down randomly

Hi everyone

Received a iphone5 into the shop with a broken screen and apparently that was all that was the problem, apparently!

Checked phone over prior to repair

Screen Cracked

Rear Camera not working

Not charging correctly: Battery Percentage would not increase so removed Battery and checked it out of the phone and it was more than 70% charged and charging so was good

Put new screen on,

Replaced Rear Camera

Started up phone and after a short time phone rebooted and rebooted about every 5 mins so did a reset back to factory, seemed to be OK then it started again, rebooting

So decided to change the charge cable flex

Put it all together and it seemed to be working fine put the phone under pressure. Started recording a Video, 20 mins did not miss a beat. Full check of phone all worked well........... 1 Hr after giving back to Client starts the shutting down, restarting thing again. Any Ideas??