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Constructive Butchery of a HP25C

Posted by Walter Gray on 2 Apr 2000, 9:51 p.m.

I bought my HP25C back in Aug. 1976, when the "C" model first came out. It cost 155UKP which would have been nearly $310 US in those days, so naturally I took good care of it. (Definitely no throwing it on the ground to see how well it bounced!)

By 1982 I was getting somewhat fed up at the way it seemed to consume Nicads. No matter how carefully I discharged and recharged them, they died like flies, and replacement battery packs were not cheap.*

Eventually I got up courage and installed 2 ordinary AA-cell holders bought from Tandy (Radio Shack) for 17 pence each. You can imagine how I felt when it was necessary to clip off the battery contacts. That was the point of no going back. Fortunately a good pair of Swedish cutters clipped through the fibreglass very neatly. Then a couple of solder connections to the PCB traces, and fix the battery holders in with a big messy blob of epoxy.

So now I can use the HP25C with alkaline cells or nicads and for a while I was notorious for scrounging dead battery packs and salvaging the good cell (there is always one good cell in every dead pack).

Now it's 1997 and the old HP is still in use almost daily in my hobby room. Despite the availability of PCs, there is still no substitute for the sheer convenience of a small handheld programmable calculator.

*Curator's note: Walter was operating under the folklore of the time that encouraged full discharge of nicad battery packs. Deep discharge of multi-cell packs can lead to short lifetimes. See the battery page for more details.

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