Very important: attempting to solder directly onto a NiCd battery terminal is

  • dangerous (the battery might explode in your face)
  • difficult (it's very hard to make a good solder joint on the battery terminal's surface)
  • risky (chances are that by the time you're done, you've seriously reduced the operating life of the battery through repeated overheating)

For these reasons, you're strongly advised not to attempt this but use batteries (available at Radio Shack and elsewhere) that have solder tabs (these are typically attached in the factory by ultrasonic welding.) Even when using batteries with solder tabs, be extremely careful; overheating can still cause nasty leaks. For instance, although I normally wear glasses, I tend to take them off when soldering small parts. However, I always wear my glasses when soldering battery packs!

Hewlett-Packard "Classic" battery packs

Under ConstructionPictures to come

"Classic" battery packs, used in the HP-55, HP-65, HP-67, HP-75, and other calculators, consist of three "AA" battery cells in a plastic casing. The easiest way to repair these packs is to obtain similar sized rechargeable telephone battery packs with solder tabs from Radio Shack or elsewhere. First, you must remove the outer plastic envelope from these batteries; just make sure you don't rip off the presoldered tabs by accident.

To open a "classic" battery pack, you need to use a utility knife. Carefully pry open all four corners of the plastic casing. Prying a bit more is usually sufficient for the case to snap open; you can then remove the old battery cells, but don't discard them just yet. You need the two original connectors in order to rebuild your pack.

Carefully cut off these connectors, cutting as close as possible to the battery terminals. Now you can dispose of the old NiCds (remember, they should be recycled as they're quite poisonous.) Carefully solder these connectors to your new battery pack, observing polarity. Make sure not to short the new battery pack at any time while doing this; they usually hold enough of a charge to cause some serious burns or overheating. This can severely damage the new pack, not to mention your hands or eyes.

With the connectors soldered in place, insert the new cells into the old battery pack's plastic shell, and close the shell. A bit of crazy glue or solvant should be used to seal the pack. Don't use too much glue; keep in mind that you may have to repeat this operation in a few years' time...

Hewlett-Packard "Woodstock" battery packs

Under ConstructionStill to come...

 Hewlett-Packard "Spice" battery packs

Under ConstructionStill to come...

Texas Instruments "BP-1" battery packs

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 Texas Instruments "BP-7" and "BP-8" battery packs

Very important: BP-7 and BP-8 battery packs contain electronic circuitry that includes a DC-DC converter that produces 9V DC from the 2.5V DC nominal voltage of two NiCd cells. If you ever operate such a battery pack for any reason with no cells installed and properly connected, the DC-DC converter circuitry will be damaged beyond repair! The symptom: the calculator will work fine from the wall adapter, the battery cells will apparently charge fine, but when you disconnect the wall adapter, the calculator will no longer function; if you measure the output voltage of the battery pack, instead of the expected 9V DC, you'll see only the NiCd cell voltage of about 2.5V DC.

Under ConstructionStill to come...