Powerbook won't charge OR run on Good Batteries despite PRAM & PMU resets

Question

Hi All, I own 4 Macs including 2 G4 1,67ghz 15" Powerbooks. I can't get one of the units to CHARGE or run OFF GOOD batteries.(Batteries charge fine on the other unit). I have tried the following:
1) PMU and PRAM NVRAM resets (Open Firmware)
2) Used the same power chord on both units. Both run fine off the power chord.
3) When I do the PMU reset, I need to reset the DATE/TIME preferences.
4) In System Profiler, the unit recognizes both batteries, one at 99%, the other @ 87%
5) Computer works fine so long as it's plugged in and the AC connection is maintained.
6) Cleaned the battery contacts o the machine
When I take the power chord and battery off the GOOD unit as if I'm doing a PMU reset and hook either the battery or power chord back on it also needs a DATE/TIME preference reset. I SEEM to recall both units always doing this, but I do have a faulty memory. The good unit holds the Date/Time with the battery installed.
The simple questions : Do the need for Date/Time resets with the batteries out of both units mean bad PRAM batteries on both computers?
The harder question: Any ideas/suggestions as to what might be wrong with the bad unit? I'm guessing ? that the PRAM alone is not the issue since the GOOD machine starts up fine despite a potentially??? bad PRAM battery.
I realize the logic board might be an issue, however the machine runs fine with AC power. I did take the computer apart to replace a faulty logic board awhile back but can't remember if the problems manifested immediately and as a consequence of that since I put the unit on a shelf and didn't use it again for 6 months or so. Is there anything besides the logic board that might be faulty/disconnected preventing the computer from utilizing battery power.
Again, it SEES a perfectly fine battery. It just can't use the battery.
Thanks for any and all input. I appreciate it.
Curtis

Answer 1

I happen to have two G4 1.67Ghz 15" PB's sitting in front of me too .... However, to answer your question ... If you remove the power and you remove the battery, and, when you put the power or battery back in and restart the system, and it resets the date to 1969 or some other ancient date, then yes, the PRAM battery is bad.
Now, the bad unit. There are 4 components to charging circuit: power adapter, dc-in card, battery, and logic board. With two systems, you've verified that power adapter and battery aren't contributors. The fact that it runs off wall power suggests the DC-in card is good. That leaves the logic board. Sadly, there isn't a test of any of these, so you have to do it by process of elimination. One of our PBs stopped charging a couple of years ago, and at the Apple store they said they start from least expensive and move up from there when it comes to diagnosing power issues.
The least expensive way to fix the logic board is to take it to the Apple store. For $350 or so (costs around 2X if done in store), assuming the case isn't banged up, they can ship it to the Apple Depot, who will replace whatever it takes to bring the system up to close to new. Comes back with a 90 day warranty. On the system we used this for, they replaced the logic board and battery, and it's worked fine, except it's recently developed the bad memory slot. For it's use, 1GB is OK, so it's not a big deal, although a bit disappointing (likely used a refurbished board that tested well at that moment in time).
Good luck!