41 Rechargeable Battery Packs


I've just been given a couple of dead rechargeable battery packs which I plan to rebuild (with 1/3AAA cells as per Katie's article 335) and just wanted to check how the packs come apart - I'm assuming that the obvious seam that runs around the middle of the pack is the seam that I need to cut?

Is it glued around the full length or just in parts?

Are there any clips or other traps I need to be aware of?

Many thanks


The following are a few notes i cut and pasted from this forum while rebuilding my own pack. My apologies for not providing proper attribution to the various contributors. The information would be available by searching the archives.

You will find some good advice below.
Best of luck,
Sorry if this has been covered before, but I'd like to rebuild a ni-cad pack for a recently acquired 41C. Everything cleaned up okay and is functional. I've read Katie's notes in the articles section on replacement cells for the pack. She states the 1/3AA cells from Digikey fit with room to spare. That's where I would like to double check with the group at large.

The original 1/2N cells are approximately 0.50" x 0.60" including the heat shrink cover. The Digikey catalog lists the 1/3AA's as 0.57" x 0.69". I'm just a bit unsure of "having room to spare" as it looks like the internal max length of the case is 0.685" and at that dimension, there are case bosses in the way. This is not taking into account the welded tab thickness as well. I'm either going to have to cut away part of the case, or perhaps Panasonic has changed the dimension specs since Katie wrote the article last year.

Can anyone explain the seemingly obvious lack of volume to me?
Sorry all, I see now Katie did say 1/3AAA, not 1/3AA. The Digikey catalog no longer lists 1/ 3AAA, only 1/3AA. My mistake.

Ah, to now turn over a few rocks to find the elusive ni-cads in question...
I have found that Gold Peak makes a 1/2N ni-mh 180mah battery. This is an exact physical replacement and 2X the capacity of the 1/3 AAA mentioned earlier. I'm still trying to track down a distributor with stock. I hope I can find some as it is a 1000 pc order direct from the factory. I'll post here when I know more. I also have to check that the HP charge rate will be okay for the ni-mh cells. Spec sheet says (slow rate) 18ma for 14hrs.

As for opening the pack, I used a plastic hot knife, fitted with an x-acto #11 blade. The case at it's thickest point is only 0.075" thick. There is a divider between the charger circuit board and battery area, so only go as deep as necessary with the knife to part the halves. It's not at all difficult.
Some years ago I got a 82120A with replaced cells from Richard Taylor (www.taytec.com ; rick@taytec.com). The cells are *smaller* than the original ones, but have higher capacity. It still works very well.

Maybe you could ak him for more info on this.

I have used Sanyo N-50AAA batteries, recently purchased, to rebuild one of the 41C packs. They are rated at 50mah. I'm not sure the rated capacity of the original batteries but these work fine. They are physically smaller than the originals, and that probably helps to make the installation easier. My only problem was that I received the batteries without solder tabs on them so making them into a pack meant spot welding tabs onto them. Soldering directly to the battery buttons would have heated them up too much, I think.

BTW, the Sanyo N-50AAA cells are NiCad.
You can open the pack by slicing around the three sealed sides with a single edge razor blade. It can be tough going but does not risk damaging the case with a hot knife. I start at the back/side seam joint and try to cut into the corners. Then I work along whatever joint seems to be going easiest. Sometimes a little tapping with a hammer helps. Wear safety glasses and keep your fingers in one piece. I use el-cheapo 2 cent razor blades from harbor freight and usually break a couple on each pack.
I started with the x-acto knife much the same way. I tried braking corners to part the seam, but it was really fused together. I knew sooner or later my fingers would pay the price, so I switched to the heated version of the same blade.

The resulting gap is perhaps a bit fatter in places than the ideal, but I figured I would stick the whole thing back together with household "goop", a sort of rubber cement on steroids. Fills the gap fine and the pack will not be any thicker than it started out due to the internal divider acting as a spacer to set the height. May not be the prettiest pack around when I'm finished , but it sure beats spending $60 on a battery pack for a $40 calculator.

I have an 82120 pack already oppened, but I was not lucky enough to find rechageable batteries that small to replace the original ones. The ones I found are big and "fatty" and do not fit in place. There is no number, they came from an assembly pack with three, to form a (almost) AA- size pack. But they are biger than the third part of an AA-size battery.

What I observed is that the pack has a small freedon of side movements (at least mine has), what leades me to think of a small, thin plastic sidewall to recompose the gaps after cutting. Did anyone observed this fact and/or tried to do something like this?

Just reasoning about it.
The hope of finding the 1/2N in ni-mh seems pretty slim. I checked with the master distributor for Gold Peak and the problem is lack of demand. It is a very low volume part and nobody wants to get stuck with a case quantity (1440 cells!). He does have about 10 original replacement 1/2N ni-cad packs made up for the 41 series machines if anybody wants them. Cost is $29.50/pack. Email me for his phone # if you want it, I don't want to post it.

On a more positive note, The Battery Station (listed under the battery section here) has Gold Peak ni-mh cells in 1/3AAA size which will fit fine. They are 120 mah, which is better than the original 70 mah ni-cads. I've ordered enough for 3 packs. That will leave me with some spares if anybody wants them. Cost was $2.50/cell.


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