XR Battery replacement work arounds!

I know a battery replacement will give my customers phone a service error msg but it was working fine until she updated the iOS causing the battery to not work only at 1% and die will not take a charge but will sync to the computer!

It will stay on when plugged in but not charge battery

So if I downgrade ios with some software 3utools will it work?

Would if i jailbreak it would it work?

In a nut shell would if I unhook battery plug in external power bank to get phone to stay on maybe powerbank case to trick the phone that it has a battery will run at 1% I dont know if it would work?