Second-hand iPhone 15 Pro battery drains fast and warms

Hello. I just got the iPhone 15 pro second hand. It was obviously reset by the previous owner to the Hello screen. I’ve noticed that the battery trains a little bit faster than I think it should and it gets a little warmer than what I think it should be. I’ve also updated to the newer iOS 26.2.1 version. Is it because the phone just restarted and it’s doing background or is it something else?