Battery charge not showing correctly.

My Poco F3 still charges however the battery percentage shown on screen does not increase from whatever was showing when charging started. When it is disconnected from the charger it continues to show the phone discharging until it gets to 0% and switches off. I then turn it back on and it jumps up to 85% charge and continues to work and discharge until it actually runs out of power and turns off at some "random" charge %. It then tries to turn back on but turns off during power on sequence. I then place it on charge and it turns back on and shows 85%. I'll leave it on charge for a while at 85% then the cycle begins again.