Battery health goes down no matter what whether you update or not. I used mine 16 hours a day with screen on and apps open for 4 months on battery most of it and it still didn’t move below 100% for 3+ months.

If the battery was at 0% for any length of time it could be acting funny. Maybe they damaged your phone when replacing the battery. Fake battery (only apple store can do this for you)?

It wasn’t the update.

Battery life is unusable below 84 imo. SE1 is good if you can get the new apple battery.

These people saying normal do not have apple certified new batteries. Take it in for a new one at the apple store and be done with it. It is expected with a used phone or phone that has not had a charge sitting in a drawer for years at 0%.

It jumps around. I lose about 1% a month as a heavy user, but it only updates every few months.

Get apple to throw a new battery in that bad boy and enjoy a few years of use