Battery percentage stays the same

I have replaced the housing and the deigitizer in my iPad mini 2. I have not yet glued the digitzer on because of the charging issue. The problem is that when I plug the iPad to change it the battery percentage stays the same. Today I plugged it in and it was on 70% and a few seconds after I plugged it in it dropped to 65%, so I unplugged it and plugged it again and it dropped to 62%. So I left it to charge for a half an hour and t remained at 62%. I turned it off and on and it was 63%, a few seconds later it went to 64%. After another half an hour it it stayed at 64% so I turned it off and on again and it was still 64%, about 3-4 minutes later it went up to 65% and then a minute or 2 after that it reebooted itself and was on 64%. I unplugged it and after about 30 seconds it went up to 67% not sure how that's possible. So I was looking thought the App Store and it suddenly dropped to 63 percent and rebooted itself and it was on 62%. I also tried a factory reset but that didn't do anything. I do not see any damage to the connector on the motherboard or battery connector. I may have damaged the battery when removing it from the old housing as i had to pry it out and it was very arkward to get out because the battery has two segments and is very big. I think this is a problem with the battery. If you know what the problem might be please let me know as I need to use this iPad and it's been broken for over a week now as I had to wait for parts. And thanks in advance to everyone who contributes and helps.