Chosen Solution
I just attempted a battery replacement on my iPhone 8, after swapping it and powering it on the device started up but no battery percent shows up in the top right corner (even though I have it on in settings) and when I plug in my phone the charging thing pops up and it says its at 0%, the percentage doesn’t change at all and the phone will reboot every couple of minutes despite being plugged in. I tried reinstalling my previous battery and now the same issue is occurring, I’m wondering if anyone else had this issue after a battery swap and knew of a solution?
You have nudged a small component on the logic board. There are two of these components close to the battery connector. They are part of the gas gauge circuit that gives the CPU information on the battery. If one or both have been disturbed you will get what you are describing.
This is the second time I have seen this question in 10 minutes. Try the old battery. Clean the connector with a qtip and alcohol. Don’t have it plugged in when you change the battery. I find it odd that the same thing is happening at the same time. Did you just update to ios 13.6
