My redmi 4a got auto restarting .and never turn on back

Hi have this redmi 4a ..it just automatic restarting again and again until it get 0℅ battery .but when i plug the charger .it backs to normal while the charger is being connected ,but if i unplugged it ,it back to restarting again ,after that it shutdown and never turn on back ….What Should i do ? Should i buy a new Battery? Please help me