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On my 286 board, the CMOS battery is missing – as with most boards of that age. I see no other battery connector on the board. However I would love to fit a battery in there, so that I do not have to enter all the settings every time. What options are there? I guess I can't just solder any battery holder in there, since the original battery was probably a NiCd rechargeable. So what are my options? Are there 2032 button cell holders with charge protection or something like that?

Also there is still a bit of corrosion on the traces as you can see. What do I best use for neutralizing it? A bit of vinegar?

Missing battery on AT mainboard

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  • You can still get the original batteries as parts. At least my local electronics store still has them.
    – fuz
    May 11, 2018 at 12:20
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    I don't recall those batteries as being rechargable ... were they? I thought they just had a very low drain to run the clock chip and that way lasted 3 or 4 years ...
    – davidbak
    Jan 24, 2021 at 19:33

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If the board does not have an external battery connector, you can try connecting an external battery pack (for example, a 3 x AA holder containing alkaline batteries) to the original internal connector. The positive lead should be connected through a diode to stop the motherboard attempting to charge the battery.

This thread on the Vintage Computer Forum is discussing a situation that appears similar to yours. It includes a diagram showing how the battery pack and diode should be arranged. There is also a recommendation to use a Schottky diode as the voltage drop is less.

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  • The link is dead. Can you please update it.
    – mikijov
    Feb 20 at 13:48
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    I have updated the link.
    – john_e
    Feb 20 at 16:17
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It is not uncommon to find a 4-pin battery connector on an AT-compatible motherboard, even if the board had a rechargeable battery on-board. Such boards would also usually have a jumper to enable/disable the battery charging circuit. If you connect a battery to the 4-pin connector you would normally disable the battery charging circuit since those batteries were normally not rechargeable.

If you can locate the documentation for your board (or its jumpers are well-labeled) you can check to see if you have these connectors.

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