Battery change first or update first?

Hi everyone,

I’m almost 3 years in with my 13 Pro and due to my fear of battery drain/GSOD few years back I stopped updating my phone. It’s currently on iOS 15.6.1. Yes, probably among a few who are still on 15 haha.

It’s been serving me very well, no issues no lags whatsoever which made me think it could serve another 2-3 years at least. However, some of my apps no longer support iOS 15 making it non functional. Since my battery health is now at 81%, I’m planning to get it replaced.

Question: Since i saw people saying updating/upgrading the iOS will cause you to lose a few % of battery health, should I replace first or update first?

Also how’s the new iOS 18.2.1 for most of you in terms of battery/performance?