New Battery causing restart every 3-5 minutes on iPhone 5 SE

Hey everyone,

The past few days have been extremely frustrating. I purchased a replacement battery for my iphone SE off ebay. It came in the mail and I took my shot at replacing the battery (I used to repair iphones in 2015-2016). All went pretty smoothly except the original battery was hard to get off with all the adhesive. Needless to say, that battery is no longer. I put in the new replacement battery and reassembled the phone. Everything seemed to be okay until the phone started to restart on its own after 3-5 minutes. There was no way to stop it and the phone was reading weird battery percentages. Sometimes 1%, sometimes 100%, and sometimes around 20%.

Since then I have ordered a new battery from Amazon and installed that one as well.

Unfortunately, the problem persists...

I also noticed my phone is a bit laggy. I'll go to my calls menu and having the names of recent calls takes unusually long to load up.. Switching begin screens also seems sluggish.

Any ideas on a possible solution?