My iPod classic 6 battery does not charge beyond certain point...

Hi!

I recently flash modded my iPod classic 6th gen (80gb) with a CF card to 128gb. Since they are pretty frustrating to open, I also replaced the battery. Since then it only charges from my computer (i used several original chargers). That isn’t a very big deal… And I also don't think this has anything to do with my real issue.

My real problem is my new battery. It does not seem to charge beyond a certain point. It charges until it’s at ‘'almost empty’'. The icon stays on the charging symbol, but every time I unplug the charger, the battery is still almost empty. I don’t know why this is.

I just tried factory resetting but it doesn’t seem to help.

Can someone please help me!

Anything will help!

Thanks in advance!