PowerBook G4 dies when unplugged

Hey folks. I just bought a PowerBook G4 off of craigslist today. 1.67GHz G4 processor, 15" screen, etc etc. The battery shows 99%, and when I unplug it I can count one Mississippi, two Mississippi, three Mississippi, four.. oops, it's dead. In the menu bar I can see it recognizing that it's switched to battery a split second before the screen goes black.

An excerpt from System Profiler, leading me to believe the battery is fine:
Battery Installed: Yes
First low level warning: No
Full Charge Capacity (mWh): 3615
Remaining Capacity (mWh): 3587
Amperage (mA): 0
Voltage (mV): 12494
Cycle Count: 274

Any ideas?

flopticalcube said:

Reset the PMU?

Click to expand...

First thing I tried. I also tried reset-nvram, set-defaults, reset-all to no avail, followed by a triple PRAM reset. No dice.

I'll ask one of my instructors who's an Apple fanatic if he happens to have a spare battery laying around.

When I restarted, it had rolled the time back to the epoch, even after I previously set it to today. I believe this indicates a dead PRAM battery? I don't have much experience with PRAM, but I know that when a CMOS battery dies, you can kiss your PC working as expected goodbye until it's replaced.

Does this sound reasonable? The previous owner said this was happening before he bought the new battery (although that doesn't explain how he cycled it 274 times, maybe he bought it used?). I figure it's worth the $5 to try it.

EDIT -
I'm giving it the Apple suggested four hours of running off the power supply without a battery installed, since the PRAM battery is apparently rechargeable. Meanwhile installing Leopard combo upgrade. I really hope the logic board isn't a lemon. Backlit keyboards aren't cool on desktops.

I left it running over night to recharge the PRAM battery and no dice, so I'm guessing that needs to be replaced. What's really interesting is that if I close the lid and unplug the power cable, then plug it back in somewhere else, it'll awake from sleep but has forgotten the system time and my wifi network, leading me to believe that main power may be fine but the PRAM is just shot.. but then main power should be holding the PRAM for me.

I can't afford a new battery right now, so I'm just going to get a new PRAM battery and see where we go from there. Anyone have a guide for cracking an AlBook open?

kbfr08 said:

If you feel comfortable doing so, you can disassemble the battery and replace the cells. It's an easy job, I did it to my macbook.

Your battery probably has a dead cell, you can actually see an air bubble in the Li-Ion cell if it has gone bad. The cells should not have any air in them unless they're dead.

To replace a cell, cut the wires for + and - and dispose of the battery properly. Find a similar mAh and Voltage battery on ebay, then solder it into place making note of the polarity. I think you need 6 cells for the battery, you could try only replacing the dead cells though. Individual cells cost about $7 each on eBay depending on the seller.

Click to expand...

Although I love being able to tell stories about potentially killing myself, I'll pass this time. I found a few on ebay for around $30.

Just as mysterious as the problem itself, I tried starting the computer today with it unplugged (I've been doing this every so often, with a teaspoon of wishful thinking) and it started up just fine. The battery is at 62% and falling, and I'm getting great battery life.

If I had to speculate, I'd say something inside the computer was extremely discharged and took forever to recharge.. or something like that.

EDIT -
The issue is back. An Apple Genius basically told me "Yeah, when a logic board is failing, it'll work sometimes and not other times."

The computer has been admitted to the Macintosh nursing home, also known as eBay. Someone else's problem. (I stated that it doesn't run off the battery)