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PB 5xx Backup (“PRAM”) Batteries

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Hi all, I looked through the archives here for any mention of 500-series PRAM batteries (it turns out that they are actually full-on 50-mAh backup batteries, not just a feeble thing for for keeping the PRAM alive), and apart from learning that they are very unlikely to leak or to stop working entirely as they are non-exploding rechargeables, the only things I was able to determine were: (1) they are physically very difficult to access if you do want to replace one, and (2) you cannot get one to charge in-circuit without first persuading the PowerBook that its main battery has charged up as far as reaching working voltage.

 

That latter point is damned awkward. I was lucky enough to receive two main batteries with my 540c, but as is usual for such at this point in history, both are stone dead. Recelling them would not be particularly difficult, but they are (at least nominally) “intelligent,” and the embedded microcontroller is not a known quantity as far as getting it to accept that its notions of prior charge behaviour need to be forgotten about.

 

Does anyone have any tricks for either (a) fooling the machine into charging the backup battery in the absence of main batteries, and/or (B) getting the main batteries to resume working after recelling? I will be very surprised if I ever am able to operate the unit on battery power for longer than a couple of minutes. I am not convinced that will ever really be an option and am not worried about it; I just want the backup battery to be useful again.

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The reason is:

"The backup battery is only 50mAh in capacity, intended to preserve the contents of memory in the two minutes of sleep time that succeed the third and last warning about low power in the main battery. It will continue to preserve the contents of memory for about a day, giving you plenty of time to replace the main battery with a charged one, or to connect the AC adapter."

This is a PB 1400 text, but the same backup battery is used.

So, one or two working main batteries would be "useful". :)

Maybe it's not worth the affort and it's easier to set the clock manually?

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It also stores boot settings. If you disconnect mains power without a working backup battery your boot settings will return to default.

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You want 1. Lind Battery Utility and 2. Intelligent Battery Recondition, I think it's called. Used in conjunction (one will sometimes work while the other will not), they will very often, through repeated attempts, reawaken a 5xx-series battery.

 

Certain models, and in my experience, certain individual machines, will not work properly without a working backup battery. The 2400c is notorious for it, but Duos can be difficult also. I have not seen a problem with the 540c, but if you are getting GLOD, chances are that the machine is complaining about not having a backup battery.

 

They are very robust, and I have seen these backup batteries revive within the past 3-4 years in multiple machines, so there may not be need to replace what is in there.

 

The 2400c is a special pain because once the backup battery does die, there is seemingly no way to recharge the little devil, because the machine won't start up properly. The Catch-22 can only be resolved by popping in fresh backup cells that have a charge in them.

 

There are Varta cells that can be used as replacements in the 2400c-- I have a thread about that in here somewhere.

Edited by beachycove

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5xx series work fine without functional backup batteries, you just lose all your PRAM settings when you disconnect from mains power.

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Yes, that’s the major annoyance. There are system extensions to take care of the most exasperating side effect (the clock always resetting to 1904), so fixing it isn’t super critical, but it’s one of those little nagging annoyances that is hard to completely ignore, you know? (I never did get around to writing my cheating cheater’s system extension that would copy everything in PRAM to a file on disk prior to shutdown, then restore that little file to the freshly blanked PRAM at boot time. Couple that little trick with an NTP client, of which I have found at least one that still works, and almost everything is good even without a PRAM battery. Outside of those unfortunate few models that can’t actually power up without working PRAM power, the only reason you really need your PRAM is if your boot disk is accessed in an unusual way and your Mac can’t actually find it without that nonvolatile hint.)

 

Plus, of course, fixing the backup battery’s lack of charge seems likely to involve suddenly having main batteries for the thing for the first time in my possession of it. I hate working on a laptop with no batteries at all; the slightest interruption to the power supply (tree falls on the power lines three blocks away and makes the grid flicker, cat sleeping on the power cord Because It’s Warm causes it to unexpectedly be pulled free of the laptop, etc.) causes you to lose everything, and under classic Mac OS you end up having to reinstall the system software sooner rather than later because it seems to have about a 50% chance of getting corrupted in some way whenever the machine is not shut down properly.

 

I have located the Lind Battery Utilities together with instructions to make them possibly even more effective via blind ResEdit tomfoolery (see http://seth.mattinen.org/notes.php?id=1),but EMMpathy and the Apple one seem to have vanished from the net (at least, hours of casual Googling haven’t yet revealed a working link to either one). I keep meaning to check the various mirrors that sprang up upon the demise of the former Apple FTP site, but I haven’t had much luck finding any of them, as only the Internet Archive one seems to have a particularly stable URL (mind you, I haven’t put much effort into that particular search yet, either).

 

All of that said, these batteries are apparently considered discharged by the power management software when the voltage across their output terminals drops to around 10 V. These ones are both registering around 0.1 V — two full orders of magnitude smaller, and at the very limit of what my cheap analogue multimeter can even register. I have to say I am not especially optimistic about their chances of imminent revival. Fortunately, they are apparently quite straightforward to recell, providing you find some way to glue the plastic shell back together afterwards.

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I wouldn't get my hopes up either, there is a point where batteries enter a state of what is essentially "permanent" discharge where there is actually a chemical change in the way the anode, cathode, and electrolyte behave. You can try to prod them back into working, but it would take special equipment, and even then, you run the right of a thermolytic reaction that will cause the battery to essentially become a bomb, so I would advise against it, unless you really, really know what you are doing.

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I can safely say that, as I know only enough to be dangerous, I probably do not Know What I Am Doing; I also do not have access to any such special equipment as you describe.

 

Assuming that 0.1 V is indeed low enough to indicate the battery may have entered a state of permanent discharge, is there any credible risk of this bomb-like state being entered through regular attempts to charge it in the machine? I now have software which could in theory revive the battery if there's actually anything left to revive, but I would rather not make the attempt if it might reduce the machine to slag in the event of unfortunate chemistry.

 

I kind of need an answer to this before I can know how best to proceed. I am not made of money and will only attempt recelling if there is no alternative, meaning I want to try EMMpathy and the Lind utilities first (ideally I'd have a copy of the Apple one to try as well), but as I said -- I only will try that if I can be reasonably sure it won't destroy the machine, which on my budget is pretty much irreplaceable.

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I can safely say that, as I know only enough to be dangerous, I probably do not Know What I Am Doing; I also do not have access to any such special equipment as you describe.

 

Assuming that 0.1 V is indeed low enough to indicate the battery may have entered a state of permanent discharge, is there any credible risk of this bomb-like state being entered through regular attempts to charge it in the machine? I now have software which could in theory revive the battery if there's actually anything left to revive, but I would rather not make the attempt if it might reduce the machine to slag in the event of unfortunate chemistry.

 

I kind of need an answer to this before I can know how best to proceed. I am not made of money and will only attempt recelling if there is no alternative, meaning I want to try EMMpathy and the Lind utilities first (ideally I'd have a copy of the Apple one to try as well), but as I said -- I only will try that if I can be reasonably sure it won't destroy the machine, which on my budget is pretty much irreplaceable.

 

Charging it in the machine? No problem, because the hard-wired safeties will kick in before there is an issue. Just don't expect to get very far.

 

The potential for molten slag only happens when one starts using exotic methods to try and get them to come back to life which either eliminates or disables all the safeties.

Edited by Paralel

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