You’ll need to do some sleuthing!
You likely have a burn’t MOSFET within the charging logic so power is not getting to the battery. Are you knowledgeable on how to read a schematic and use of a DVM? If you are you’ll need to find the schematic and boardview drawings of the main logic board to probe the power rails and test the MOSFET’s.
Your other opton is just replace the logic board [guide|528]
Now the hard question! Is it worth the investment?