iPhone 7 battery replacement gone wrong

Hi folks,

I replaced the battery on an old iPhone 7 my sister used as her daily with one from iFixit and after reassembling everything and turning the phone on, it began boot-looping. Disconnecting the home button flex cured the boot issues but the phone now overheats and a full battery drains in a matter of minutes (seems like an audio IC failure).

I've repaired a fair bit of iPhones (older and newer) and this is the first time it goes so wrong. I have no idea why the home button or its flex cable failed and why the phone seems to be displaying logic board issues too. It was working perfectly fine before I opened it.

Carefully removing the screen is the first thing I always do and I take great care when disconnecting/connecting all flex cables. I've read that iPhone 7s had notoriously fragile internals. Is it true?

What could I've possibly done wrong to mess up this repair so badly? Just want to learn from whatever mistakes I've made or if I just had bad luck with an old and fragile phone.