HP-25 battery pack


I recently acquired another HP-25, actually in working condition, minus the battery pack. Does anyone know where I could buy a replacement battery holder? I don't need the batteries as AA NiMH batteries work just fine.

Failing that has anyone built one from scratch?


I've thought about trying to cast these in polyethylene resin for my use. Would there be a wider interest? I've only got two woodstocks & one battery holder. However one of the calculators isn't 100% reliable so my motivation isn't high.

Prices at auction for obviously broken calculators with intact battery holders seem insane.

- Pauli


Good idea Paul!

I thought of making some kinda mold and casting my own, but didn't know what plastic to use. So if you make some I'd be happy to buy one or two off you!

Another idea I was toying with was to make one out of hardwood. It'd be slow, but with patience I reckon you could to it. Wood would be strong enough for the job easy. I'd make for a special looking battery pack too!


I'd use Easycast if I ever do do some. It should be strong enough and it is quick and (relatively) painless to use. If it isn't up to the task, at least the moulds would be ready for experimentation with other casting compounds.

Wood sounds like a very interesting idea. It would be very slow and painful I expect. I've done plenty of woodworking but not any wood carving so I'd rate it beyond my current skill set.

- Pauli


This could be a solution; if only we could get Jay into old calculators. If not; my suggestion would be to wait a couple of years till this technology is at every street corner. When 3d printing becomes available at affordable prices it will change everything.


I believe this works only with solid pieces, as you must scan the exterior surfaces on all sides. In the case of the battery pack, as a minimum you would have to split it into 2 separate parts. Also, you would have to fabricate a spring to maintain pressure on the electrical connection with the fixed contacts on the calculator and to provide continuity with the two battery cells. Quite complicated, actually.


Casting the battery pack will require two pieces and the spring too.

- Pauli


Wood it is then!

It'll be fun even if it doesn't work out. Everyone needs a summer pastime. This one is mine. Too hot outside for much else.


The thing about Woodstocks is that swapping out a battery pack is super easy, so I simply share among the various models, except the HP-25c and HP-29c so that I don't lose the programs.


Would be great to get Woodstock battery cases, however, I am afraid, tooling for plastic injection is pretty expensive. Since I am in the same situation - more Woodstocks than battery cases - I help myself with handmade cases from standard AAA battery cases, which are cheap. With basic tools they can be converted into a Woodstock battery case, not so beautiful, but functional.


Edited: 28 Nov 2009, 8:33 a.m.


Do these stay in without tape?

I wouldn't injection mould - way too expensive. Making a mould out of silicon rubber is pretty straightforward and casting in polyethylene resin also.

- Pauli



No tape, the battery cases are just kept in place by the spring force. A mechanical lock as with the original ones would be better of course, some day I try.


Edited: 29 Nov 2009, 5:05 a.m.

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