IPad 5th gen battery issue

Ok so I had a guy bring me an iPad 5th Generation in to my shop with a cracked Digitizer to get repaired. While testing it I noticed the battery shows 1%, so I plug it in to charger and once the charger recognizes it shoots to 100% and will stay on for about 10 seconds then shuts off and turns back on at one percent, within a few seconds shoots back up to 100% and just keeps cycling through.

It was doing this prior to working on it, I went ahead and replaced the Digitizer but cannot figures out what could be causing the issue.

Do you think it’s possibly a bad battery? Software? It has an update available but shuts off before it can update, thought about trying through iTunes but don’t want to do that and then the iPad get stuck in recovery if it shuts down in the middle of an update