Battery Drain and overheating while charging

My kid dropped my iPhone 7 from our 3rd story flat a couple of months back. There were a couple of barriers due to which it wasn’t a direct fall. Also, it fell into wet sand. Basically, there was no damage at the time. Nothing visible and the phone had been working fine for past 2 months

Last week, the battery drained pretty quick ( in about 4 hours). From that day onwards, no matter what I did, ( reinstall, DFU, fresh install with nothing installed on the phone), the phone discharges in 12/13 hours if left on standby (aeroplane mode, without a SIM or WIFI) and within 2-3 hours of light use.

I changed the battery, unfortunately that didn’t help. It still drains in 12-13 hours in standby and 3-4 hours while usage. I am not sure where to go from here, any help would be greatly appreciated.

EDIT

I switched off the phone last night before going to sleep. Battery at the time was 69%. When I woke up 7 hours later and turned the phone on, it had drained all the way down to 6% ( while it was turned off)