iPhone rebooting loop several months after battery replacement

Hi,

I bought a battery from iFixit several months ago to fit in an iPhone 5s. The battery developed issues and would no longer hold a charge. I contacted iFixit, and they agreed the battery was defective and sent a replacement.

A few more months down the line, I think I'm having the same problem with the replacement battery. When attempting to charge the phone, it will boot to the lock screen before shutting down and booting again. It will only power-on when plugged in.

Could I have two defective iFixit batteries, or is something else happening?