Question about PowerBook 1xx series cells

[beachycove]

Having had some recent successes in re-celling Duo and 5xx-series batteries, I just opened a PB1xx series battery, expecting to find something like 5 x 1.2v NiCd cells for 6v (like the ones you see being sold newly recelled with NiMh cells from battery retailers).

Excuse my ignorance, but what I discovered instead and do not quite understand was what appears to be 10 x 4/5 AA NiCd cells in the battery. Is this what is found in all original PB1xx series main batteries, and if so, what is the voltage and the likely mA rating of the individual cells? Surely not 0.6v?

I am, I think, going to have a go at recelling with fresh cells, just to make the old PowerBook work like it is supposed to, but I first need to know what to put in there. (I think, by the way, that I will go with NiCds rather than NiMhs.)

I might add that it was not the stock Apple battery (e.g., M5417), but one from a third party company with a little extension at the side and a light, and that the cells had long since started to leak. It was rather nasty in there, so I might instead open up an Apple OEM battery instead, as I fear that the works in the one described have long since been eaten by the chemicals.

 

[wally]

Likely a series-parallel connection of 1.2V conventional cells. Two instances of what you were expecting, connected in parallel. See the handy reference at http://support.apple.com/kb/TA32393?viewlocale=en_US for total capacity of the pack.

The white stuff growing out of the battery seals is mostly potassium hydroxide, which has a way of dissolving human tissue, and can blind you if it gets into your eye. It is very soluble in warm tap water. So if you need to investigate further, put on eye protection and protective rubber gloves and wash gently under the tap as not to splash. Properties similar to drain cleaner lye, just potassium instead of sodium.

After washing the remaining ugly deposits will be mostly relatively insoluble hydroxides and some carbonates that form when the white stuff gets out of its original containment and starts corroding any nearby non-precious metals. Best not to get these irritants in your eyes or lungs. So if you ever try to clean up NiCD or NiMH leak corroded battery holder contacts with a Dremel or similar tool, just remember not to get too close to the dust created and blown about by the tool.

 

[beachycove]

I guess that would be it. But 5 1.2v cells would do for re-celling purposes, especially as they are higher capacity?

 

[wally]

My guess would be that the original designs charged at between an initial C/2 or C/4 rate (taking 2 to 4 hours to charge) then switched either to a slow trickle rate or stopped charge altogether. The trickle rate (If any) is probably between .01C to .03C where C is the spec'd capacity of the original Apple battery.

When a series parallel configuration is scrapped and a single string substituted, consider the following possible issues, which suggest some measurement and analysis and/or some experimentation:

1. The internal resistance of the single string (of modern cells) might be higher than the original two string series parallel design. This could make a voltage monitoring gas gauge misbehave and seeing more voltage drop earlier in a discharge, declare empty too soon. In an extreme case like using just one AAA string, there might be so much drop that the PowerBook would declare empty immediately. Internal resistance varies between battery cell vendors, and some vendors feature alternative designs within the same physical package dimensions, one with lower resistance but less capacity, and another with higher resistance but increased capacity.

2. One string rather than two would absorb the entire rather than approximately half of the initial charging current. Unlike fast charge RC and power tool chargers, the PowerBooks probably charge slowly enough that doubling the current by cramming all of it into a single string made up of cells of about one half the original specified total pack capacity would not fry the cells. But the voltage rise again due to internal resistance might cause the voltage monitoring gas gauge to declare nearly full too soon. Then it would take a much longer time (like as much as a day) to really top off the battery at the trickle rate. In an extreme case like using a single AAA NiCd string, if the capacity is too small the initial charge current might overheat then vent the cells, or declare the cells full charged much too soon, possibly immediately. When the white stuff has mostly vented from the original cells, they start behaving like really undersized new cells, and eventually when all the white stuff vents they act as nearly open, no connection (unless they short first).

3. One string rather than two will see and have to absorb all, not half, of the trickle charge current. The trickle charge current contributes a lot to the eventual appearance of that white stuff, but is tolerated if it kills the battery much slower than just daily cycling of the battery does. If you charge then unplug the AC adapter no problem, but if you mostly operate and store with AC adapter plugged and powered the new single string might meet an eventual venting death twice as fast than a two string series/parallel recelling (this might be several years).

So if you can match (or somewhat exceed) the original amp hours capacity with a single NiCd string that physically fits and the internal resistance is low enough, no problem. If you find batteries of slightly increased capacity but use only half of them, experimenting may be necessary to see if both charge and discharge performance is acceptable. Depending on time spent on charge, some diminishing of long term life might occur in a single string recell. If you go way lower in capacity than the original design, even as a temporary bench test, the initial charging current might be too much, and heating followed by alkali steam venting might soon follow unless the PowerBook charger is smart enough to detect an over-voltage, declare full charge and go into a protect mode.

 

[beachycove]

Not having any NiCd cells handy, but having a disused set of 10 tabbed 2300 mA NiMh AA cells soldered in series and just lying around from a failed attempt to re-cell a Duo battery (the failure led me to use 4/5AA cells in the next attempt), I separated the cells and temporarily wired 5 NiMh cells into the 1xx battery pack, along with the little thermal thingie from the Duo pack (as it was already there between the cells, and as I happen to be watching the thing all the time it is plugged in).

All tests done on a PowerBook 150. Yes, I know, but alas, I do not own a 180.

The NiMh cells, truth be told, had been tortured to within an inch of their life by a soldering iron in my original attempts to re-cell that Duo battery, largely because I found it impossible to fit the ruddy things in there over several attempts, and then they had been left unused for about 18 months. The first couple of cycles went as follows, and more or less exactly as Wally had speculated: "full charge" was reached within about 3 mins, and full discharge within 60-90 seconds. Before going to bed, I charged the battery up again and then left the machine asleep on battery power overnight.

It was still alive in the morning, but on waking, it shut down immediately through lack of power. I plugged it in and rebooted with mains power, and the battery this time charged for a good 2 1/2 hrs, and gave me about 45 mins. of runtime. I did this while running Battery Amnesia (which cranks everything up to full power - avoiding any screen dimming and the like), which drained the cells again until the machine shut down. It then charged for another 2 1/2 hours and I am in the midst of cycling the battery again. So far, it looks about the same as last, but we'll see. It would be normal to expect that NiMh cells would improve with a few cycles.

It strikes me that if this works, then Shangri-La is at hand, as it would be possible to glue in a couple of AA battery trays (a 3 and a 2) wired in series and then simply pop in standard button AA NiMh cells as required, say a set of 5 at 2800 mA.

The battery plastics, which have to be separated to allow removal of the original cells, could be left unglued (as in my jury-rigged main battery at present), as the PowerBook itself holds the arrangement together without any trouble. Use of standard battery trays would also obviate any problems that might result from having NiMh cells shaking around in an otherwise half-empty battery pack — not a good idea in terms of keeping them soldered together, but more importantly, representing a considerable fire hazard.

However, I haven't gotten that far yet. Counsel is still welcome. E.g., I see from searching this Board that opinions differ on whether NiMh batteries can be substituted for NiCd cells, and so, just for the present, I don't think I will leave it plugged in unattended.

 

[beachycove]

... it would be possible to glue in a couple of AA battery trays (a 3 and a 2) wired in series and then simply pop in standard button AA NiMh cells as required, say a set of 5 at 2800 mA.

Or get one of these.

 

[beachycove]

After a few cycles, I am now getting 80-85 mins. under Battery Amnesia with the five cells. Real use battery life use would, of course, be better, as Battery Amnesia turns off all energy saving features.

I am very pleased with this outcome, and think I will try one of the 5-cell battery trays when I get a round tuit.