Replacement rechargeable NiCad batteries for an Epson HX-20


My Epson HX-20. Cute isn't it.

I'd always wanted one of these and considered myself lucky to acquire a unit in such good condition complete with tapes and a printer unit. Everything seemed to work. I could write a BASIC program, record it to tape and even print it out. Sweet!

There was just one problem. It came with a long-deceased battery pack. This thing would not hold a charge at all. Not surprising given something that was made in 1982. Unfortunately these days you can't just go down to your nearest friendly Epson centre and buy an HX-20 battery pack so I had to come up with some kind of replacement unit.

First attempt- A four AA NiCAD Pack

My first thought was to use a four AA-battery cube type holder, stock it with 4 x 1.2v NiCADs and clip it up to the battery terminals. I experimented with this but discovered the pack was just too fat. It was too high to fit in the holder and allow the holder lid to be screwed on. Back to the drawing board.


Figure 1. A 4-battery AA pack. Too big for the compartment

Success with the second idea. A Sub C NiCAD pack

With some suggestions from friends, I decided to make a "pack" using 4 x 1.8AH SUB C batteries soldered together in a 2 x 2 arrangement. This involved taping two pairs of batteries side by side with the polarities of each pair reversed. I soldered a wire across the bottom of the batteries in the pack (from -v to +v terminal) resulting in all 4 batteries being connected in serial. I then soldered the top of the pack to the battery leads.

Sub-C NiCAD batteries as a replacement battery pack for Epson HX-20

Figure 2. A replacement "pack" made from four Sub-C NiCADs strapped together and soldered in serial

Getting the batteries into the cramped battery compartment in the HX-20 was a tight squeeze but they fitted. It was then on with the battery compartment cover and reassembly of the machine.

The improvised rechargeable battery works just fine! The HX-20 is now as it should be.

17th June, 2010

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