Powerbook will not run unless plugged in

Question

my powerbook g4 12" will only run off of the power adaptor. the battery seems okay. it reads as charged. and coconut battery shows a full charge (albeit with reduced capacity after 100+ cycles.) however it will not start up from the battery. and if it is running, and i unplug it at the unit, the computer dies instantly.
upon plugging it back in, it will start up fine. but my date and time settings are erased. and it runs fine on the power adaptor. but suddenly, this power issue happened, and it's like the battery is not even there.
so i bought a new aftermarket battery. everything seemed to go as normal. while doing the initial charge, the plug light on power adaptor glowed yellow. when i woke up the next morning, it was green. and after startup, the battery read as fully charged.
and then when i unplugged the power adaptor, bang! dead!
so, no change with a new battery.
the power does seem to make it to the battery, since the new battery did charge. but the unit will not operate off of a battery. even for 1 second.
i've done the pmu resets, and cussed some. neither helped.
help!

Answer 1

Welcome to the Apple discussions.
The reason the date resets to ancient times is due to all power being removed from the system. The 12" Powerbook doesn't have a battery to retain those settings like the 15" and 17" Powerbooks.
There are only 4 components in the electrical circuit: Power adapter, DC-in card, battery, and logic board. From the sounds of it, your power adapter is working, the DC-in card seems also to be working since power gets to the system to run it and the battery seems to charge, the battery, especially with a new one, we'd assume is good, and that, unfortunately, leaves the logic board. There isn't a test to see what might not be working in the power circuit, so you have to eliminate things to hone in on the issue.
You can't repair a logic board, so if you need your system to run on the battery, you'll need to replace the logic board. You can take it to an Apple store, and if the case isn't bent up, they can send it to the Apple Depot, which for me was in Houston, where they'll replace just about anything needed to make it almost new, for around $350. We had a Powerbook sent off for a new logic board, and they also replaced the battery (hint, if you take it to Apple to be sent to the Apple Depot, include your oldest, even if dead, battery). If the case is banged up, they charge more since they'll replace the case. If you want the Apple store to replace the logic board in the store, that runs about double sending it to the Apple Depot. Or if you're good inside a computer, you can buy a used board and change it yourself. Took about a week to get it back from the Apple Depot, and it comes with a 90 day warranty.