Battery won't charge

Hi ifixit community, hoping you can help me on this one - I've been struggling to get this thing working for a long time.

I replaced a water-damaged Macbook (mid-2008) logic board and it now works, however it doesn't work properly when the battery is plugged in.

I figured it just needed a new battery but even the brand new battery does not charge in the Macbook nor does the Macbook function properly with it plugged in. With the battery in the screen doesn't seem to display correctly.

Remember the Macbook works fine off the wall charger with no battery installed.

I tried replacing the battery connector hoping that would fix the problem - it did not.

What component still needs to be replaced to get this to work? Do I perhaps need to replace the inverter? I think I heard something about that in the Macbook troubleshooting guide.