Battery drain after iOS 15.7.5 update iPhone 7plus

Graham ~ The long process of applying an iOS update to an old iPhone with a weak battery can be the proverbial "straw that broke the camel's back." 80% is not healthy and is consistent with battery drain. Apple recommends replacing the battery at around 80%. So have the weak, aging battery replaced and all will (probably) be well:

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My original SE battery is at 94%. I bought the phone new last year. I installed 15.7.5 yesterday, and now the battery is draining down 50% in just four hours. In settings I do not see any apps that are causing this.

My 7+ battery health is 100% which was recently replaced in November 2022. Still battery drains in minutes and behaves abnormally. 😢😭

It took about three days to process whatever it does after the update and now it is back to normal. It has never drained so fast after other updates. 🤨

iPhone SE (1st gen)battery is draining causing a restart after update to iOS 15.7.5. Battery health shows 83%.