The battery circuit of your Galaxy S4 has gone faulty.
As this is a hardware issue so it cannot be resolved by factory reset or reboot.
will it be ok with a new battery
Is your phone still under warranty period of one year?
Yes this issue will be resolved once you change the battery. As your phone is still under warranty so you will need to contact Samsung Support Center and get it replaced.
got it from carphone warehouse was told I would lose the phone for a fortnight while it was at the Samsung support center.what if I take it to a mobile repair shop would this resolve the problem.
Yes the issue will be resolved by the mobile repair shop but this will not be covered under warranty. Samsung's contact number is ***** SAMSUNG (726 7864). I would recommend you to call Samsung and ask for the procedure for repairing your device which is in warranty. Else you can get your phone repaired by the local mobile center.
cant really afford to lose the use of my phone for a fortnight
thankyou very much.