Hullo goodevening,
how long have you had the phone for? is it always on charge? when do you start charging it from? 10% or 70%.
could be a battery fault or physical problem if so then replacing it would be the easiest option.
other quick tests could be ***Battery Calibration:***
* Let the battery drain completely until the phone shuts down.
* Charge it to 100% without interruptions, then restart the phone while it's still plugged in.
***Reset the Phone:***
Perform a factory reset (after backing up important data) to rule out software problems.
only do this if you have a backup but make it a last resort
Use apps like AccuBattery to check the battery's health. its not perfect but could work
goodluck