Battery not charging - should I reset PMU?

A PMU reset won't hurt anything, so it's worth a try, as the PMU can affect charging. A reset does not affect the hard drive nor the data therein.

However, I'm a little concerned that something is seriously amiss inside the battery itself. Your SP report shows zero cycles. Even a new battery shows one, so that a concerning observation.

Try this: turn off the computer; remove the battery; leave the computer powered off but on wall power from 24-48 hours. There is an internal backup battery that when dead or weak, can cause strange issues. It's technically rechargeable but, with the main battery in place, little power gets to the backup. Removing the main battery lets the internal see if it can pick up enough charge to overcome some of the problems

Yes. the PMU reset can do no harm and is quickly accomplished, so do it first. Hopefully it will save you the 1-2 day wait of the other method!

The current at those contacts is pretty low; computer components normally don't like high voltages or currents. We're not talking hauling the computer around while the battery is out---it should be OK simply sitting while the power is connected. If you are worried about the contacts, put a non-conductive mat (like a plastic placemat) under the computer and set it somewhere away from curious children, curious child-like adults, or pets.

Is this the original battery that came with the computer? If not, is it Apple-branded. If the original, it could be dead of old age or lack of use. The latter causes more premature battery deaths than you can imagine.

Again, reporting zero cycles is a big red flag for me, indicating that the battery may well be beyond the aid we mere mortals can provide.

It's the original battery.

Might think about a new one, then.

I rarely used it on battery alone

That phrase has been part of many posts about prematurely dead batteries both in this forum and the MacBook Pro forums.

There are some battery scams out there on auction sites so I would tread carefully. I trust Other World Computing--have done scads of business with them over the last 15 years--and I found a very nice batter yfoe a G3 PowerBook fomr Global Batteries. Apple no longer sells PowerBook batteries.

The battery type to oder depends on models and screen size; post if you need some help nailing down your exact model.

Assuming the battery is completely dead, would I be courting any kind of disaster by just not replacing it?

Not if you approach it intelligently, and that's obviously no problem for you. At end-of-life, some batteries may swell and/or leak. As long as you check for that possibility regularly (min once a week--twice better), I doubt you'll have a problem. Were you to be traveling and leaving the computer at home, I would remove the battery before departing--you know how things around the house tend to go south when no one is at home.

Intel Mac notebooks clock back the processor significantly when used on A/C with the battery removed. I've never seen this mentioned as a strategy used in the PowerBooks; even if you eventually have to remove the battery due to damage, you shouldn't have a problem with performance as long as you have the compuuer running.

Battery information is unchanged from my original post except that voltage is now 5970 mV (down from 9071 - should I be concerned about that?).

It's beyond hope anyway--I wouldn't lose sleep over it.

Here's some similar posts from the ifixit.com site http://www.ifixit.com/Answers/Device/PowerBook+G4+Aluminum+15%22+1.67+GHz?search =battery+charge

When you boot up from the AC adapter (and not connected to the internet), do you get a message about the Date/Time not correct. If so the internal PRAM (rechargeable) battery has discharged or is no longer good (will also need to be replaced). The ifixit.com site has the instructions.

When you store or plan to not use a laptop for a period of time, make sure the battery is charged to 40-50%, and not 100%.

 Cheers, Tom 😉