Musings and comments about our common interest
By now, all original batteries made for Tomcat machines and HP41c printers cannot hold a charge anymore. There are several replacements in the market, all of them using the ubiquitous Sub C batteries, in different energy capacities. These batteries are cheap, and most of the packs are held in place by some rubber foam corners and adhesive film. You can find them in eBay mainly.
I have tried to break apart two one of the original batteries that I have, to refurbish the original cells for new, current cells, but it was impossible without doing a lot of damage. This cannot be the right way to do more than one of them, and forget about series production! So we decided to make our own case
We have designed a two-halves case for these batteries, with precise holes for the connectors, to be 3D printed. Here the main challlenge is the cost of the parts in any 3D provider: it is far too expensive and it eats most of the cost. The parts are clipped one onto the other - and like the original, it is a single part used for both sides. We have not decided yet whether to offer it as a kit or send them fully assembled - I am quite frightened with batteries as opposed to passive, non-energy storing parts. There would be some soldering involved, in order to connect the cells among them and to the terminals.
There may be still some work to do in optimizing the part to reduce material - I can see a couple of areas where material can be taken out. However is the sheer size of the piece that determines most of the cost, I think.