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Thread: Epson PX-8 battery options

  1. #1

    Default Epson PX-8 battery options

    First, does anyone know the type or part number for the main battery connector?

    Second, can you use NiMH instead of NiCD? I'm a little tempted to try to fit 4xAA in there if it might, or 4xAAA if that is all that could be.

    Any thoughts on the AUX battery? Should it be changed/replaced to prevent leakage? Can it be operated without it? There is a switch in the battery compartment, does this enable/disable the aux battery?

  2. #2


    Also, someone removed the main battery already, and in the multi unit, they removed the batteries as well. Maybe they removed the aux battery too...

  3. #3


    The mainboard still has the aux battery on it - it does not look like it has leaked - should it be removed?

    Any problem trimming back the flexible silver ground over the ROM's chips? it is annoying to pull out of the way.

  4. #4


    The aux battery was absolutely dead as expected, I cut it from the board and removed it. Depending on what battery solution I come up with for the main bay, I may try to find something to replace it and solder some wires to the main bay or even put something where the old one was. I folded back the silver ground sheet so I could bring it back if needed. 4xAA will not fit, I think it is supposed to be 4 sub C cells.

  5. #5


    I bought four sub-c nicd batteries with solder tabs off ebay to replace my battery. They work well, although it seems a tighter fit in the compartment than the original. I also bought some connectors. I guessed at what they were and apparently got it right. I would have to do a bit of research to find out what I ordered. Are you in the US?
    I saw your PM and will respond as soon as I get a chance.
    One Important thing about the PX-8: DON"T OPERATE ON CHARGER WITHOUT BATTERY. The battery acts as a voltage regulator for the charger. Using the charger without the main battery subjects the computer to the full charger voltage.
    I haven't replaced the aux battery on mine. It seems to still work, at least somewhat.
    As for the foil, I don't think it would hurt to trim it back. I haven't tried it myself, though, so that's just an educated guess. It is primarily for RFI shielding, so you might get a little bit of TV and radio interference by trimming it.

  6. #6
    Join Date
    Jan 2014
    Northfield, MN USA


    Not familiar with the PX-8, but I have an HX-20 and it uses Ni-Cad sub-C cells.

    Those were easy and cheap to pick up. I didn't want to try NiMH or anything else, since the charging circuit seems pretty primitive and I didn't want to introduce any unknowns. My HX runs great now on new batteries.

  7. #7


    I hear you; I was tempted to just do the same thing too (NiCd), but I thought I would try the NiMH and see what happens. The PX is supposed to have a voltage cut off for the fast charge according to the documentation. One issue I still need to figure out though is which is a better voltage when using a switching adapter instead of a linear one. I don't have the original power supply. I guess the original is >9V open, 7.5V @ 150mA, 6V @ 600 mA and it is used primarily to charge the main battery pack, but also the aux battery too. I could get a 6V, but then it is only 6V always and I wonder if that is good enough to charge the NiMH well enough. I could get a 7.5V, but will it be too much? The trickle charge on the main pack is supposed to be 40mA, so probably not, but I'm not sure how much the aux battery gets.

  8. #8
    Join Date
    Jun 2016
    Guisborough, England


    For some years now I've been keeping my HX-20 operational using 4 @ large batteries NiMH externally (D cells). If I wanted to fit something internally I would need to try to make a new pack from 4 @ sub-C cells, or 4 @ AAA might just fit.

    I still have the original charger, which seems to work OK with the NiMH, although I leave it charging longer, and the charge does not seem to last as long, and the batteries don't last as long, but cannot have everything.

    If I measure the voltage across the batteries during the charging it's about 7.5v, as noted the original charger is not regulated. I've never tried testing the current. The HX seems to work OK while charging, and when charged. The HX does not have an 'aux' battery. I'm pretty sure the main battery is active at all times, and must still do something even when the unit is totally 'off' due to battery level being too low, as anything in RAM is preseved.

    Vintage Devices: Epson HX-20/TF-20, Amstrad PCW 8256 (with extras), 386 and 486 PCs with 5.25 and 3.5 floppy drives, Pentium 75 with Roland LAPC-I midi card

  9. #9


    Well, a closer look at the way the PX-8 works and it looks like it is meant to operate on an unregulated battery voltage. I'm a bit concerned about the maximum NiMH voltage vs. maximum NiCD voltage.

  10. #10


    A big thank you to interstate batteries today. They actually had the proper NiCD cells, even the small 1/3 AA ones that it takes to make the internal AUX battery. They were even kind enough to spot weld them together in the configuration I needed.

    I charged them up and resoldered the aux battery back into place. I turned it on and I can see voltage on various terminals on the PCB such as VB. Here is the odd thing though. I thought the aux battery was supposed to keep the system alive in case the main battery fails, but if I unhook the main battery, I have to press the reset button on the bottom to reset it - despite there is a voltage from the aux battery. Any ideas why this would be?


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