Phone cannot determine percentage/shutdowns(Changed the battery twice)

I have replaced the battery in my iPhone SE with two new batteries, both unable to work out how much charge there is (sometimes stays at 1% and changes when I plug/unplug the charger) The first battery I used made the phone restart (even while charging) every 3 mins or so, the battery I’m currently using is staying around 58% and is telling me to service in battery health. Both batteries were from eBay and I’ve tried basic troubleshooting like a software reset, updates and checking that the connectors are pressed in properly.