iPhone 6s hot corner, very fast battery drain.

Hi,

So i got an iphone 6s that was sitting around for like a half a year unused but working well before and now i want to give it to a family member. When i booted it up i noticed that the battery is acting strange and top right corner,1-2cm below camera, probably cpu, gets quite hot, really unpleasant to hold in hand . From 100% to 60% the battery works well, but then it gets random, for example: it goes from 60% to 50% in 1% drop like every 10 seconds or just jumps from 60 to 55, 55 to 50, then at 50% it turns off, immediately boots up by itself and then shows 10%; i use it for a half a minute it restarts again, shows 1%. I charge it up to 100% and the same story again. The phone was factory reset 2 times. Was tested at ios 13… and now its on ios 14.4. What could be the problem? Is the battery faulty? Cpu shorting, getting hot and draining the battery?