That the battery charges in the VST charger is absolutely key. It can't be a bad battery. Now I am no expert, but I would probably try the following:

• unplug backup battery and make good and sure that the power manager is reset;
  try recharging the battery in the powerbook on startup
  if it doesn't charge after that, then a faulty charge board is indeed the likely culprit. I have read in the past that the symptoms are consistent with what you describe.

Mind you, I have found Wallstreet batteries in general to be a real problem, repeatedly and over the years, even when relatively new. You might well wonder, for instance, why a Battery Reset utility was necessary in the first place ….