Battery Drains while in use, charges when turned off.

I bought a used 17" G4 Aluminum missing a battery and hard drive. I replaced the battery, hard drive and charger. Once the battery was fully charged I began installing OSX 10.4.5 Tiger. I was half way through the install when the battery went dead, wiping out the new hard drive. I closed the lid and left the charger on and the battery came back up in several hours.

Booting the computer after that showed a gray screen and that's it. I ordered another hard drive.

Installed new hard drive and installed the OSX again, this time selecting not to install all the languages. The OSX installed but the battery was dangerously low. I shut down the computer and let the battery recharge.

I knew by then I had a power management problem. Battery charges only when computer is off, even tho showing the plug icon on the monitor. So I reset PMU and PRAM, several times.

Now the computer seemed to be losing power more slowly so I set out to update the OSX to 10.4.11 via 758MB Apple update.

Watching the battery monitor I saw that before I had downloaded even 100MB of the program my power level was about 50%. Keeping an eye on it but continued download was a mistake. It dropped like a rock to 33%, then 15%, then 5% before I shut it down with power

button. Apparently it continued to drain because after charging for several hours the battery was still 0%.

So I ordered another battery, installed it and charged it up. Same problems of course, but now charger kicks off when battery is up and will not reset to charge the battery when it goes down. Plugging in another charger powers the battery back up

This is growing long and tiresome. I have ordered a used logic board and a used PRAM Battery Board. But before I tear this down to the case, does anyone have a clue as to why it charges only when off, and depletes the battery rapidly when turned on?