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Hello i have got an iphone 8 with broken screen and battery reported as « service ». I don’t know the history of the phone. I changed screen but before this i couldn’t turn off the phone since i couldn’t slide on top of damaged screen. I notice that the battery even in a poor condition (bad looking) was suite good enough to power the phone more than 5 days (the delay i got the new screen) without being exhausted . When i replace screen and battery, i observed that battery charge was quite slow. After one night it was charged at 100 %. And since it is stuck to 100% !!! Nothing changes , i found an infinite battery!!! This is quite painful to be blind on battery remaining capacity. When i charged it even with 100 % , some current is consumed (proportionnally to the previous usage of the phone). with the old battery i can’t charge it more than 37 %. do you thing it from the bsttery or from main board. (The main board doesn’t look to be a virgin board) thank you

This is not uncommon with aftermarket batteries. Some of them don’t communicate properly with iOS, probably because they have lesser quality Gas Gauge IC’s in them. As you said, contact your vendor and see if they can send you another battery.

Plug into a Mac with Coconut Battery installed on it to ascertain the actual state of the battery. https://www.coconut-flavour.com/coconutb