One of two things are going on here.
1) The battery has gone bad and it needs a replacement
2) The phone has experienced a *glitch* and needs to go through the hard reset process.
I didn't see you're phone model listed so try doing a net search for the reset process before getting a new battery.
Worse case scenario is that you have other hardware damage on the upside when you go to get your battery replaced they will do a diagnostic to assure that's the issue.