Logic board drains new battery right away touch 6

Hi,

I have a couple ipod touch 6's that were completely dead - showed no signs of life. If anything at all - one of them would show it's charging when it is plugged in ( still does ). I replaced the battery with a brand new one ( i bought 10 since I had a few ipods ) and checked them all with a battery checker and voltage meter and all are good.

My issue is when I solder in the new batteries, nothing changes - they are still dead so obviously it's not the battery.

Anyone have any ideas to what it could be or ran into this issue before?

Any help is greatly appreciated.

Thank you,