Looking at the pic, there's a 4-pin connector immediately next to the AT power connectors, with a jumper JP3 under it. That looks a lot like an external battery connector (I'd expect + on pin 1 and - on pin 4), with a clear CMOS jumper.

From the picture it looks like this board could be using an external battery pack. Next to the right of the power connector is a 32.768 kHz crystal that could belong to the RTC. There is a pin header right next to the AT power connector. What does its label say?

dionb wrote on 2025-08-25, 10:10:

Looking at the pic, there's a 4-pin connector immediately next to the AT power connectors, with a jumper JP3 under it. That looks a lot like an external battery connector (I'd expect + on pin 1 and - on pin 4), with a clear CMOS jumper.

Thanks for replying.
Yes I have also reflected about that one. Can I somehow check if it is + on pin1 so I dont fry the motherboard?
So you mean that JP3 is the clear cmos jumper?

technokater wrote on 2025-08-25, 10:12:

From the picture it looks like this board could be using an external battery pack. Next to the right of the power connector is a 32.768 kHz crystal that could belong to the RTC. There is a pin header right next to the AT power connector. What does its label say?

Thanks for replying.
It says: 1 JP1 4
Do you know if it is 3,6V or could i use a CR2032 with 3V?

In the case of external battery packs, I've only seen those with 4 x 1.5 = 6V AA batteries used for old 386 machines.
The disadvantage is they can leak, and don't last as long as the button cells. Sometimes you can see double 3V cells stacked in a suitable holder, but this board does not have any prepared space for such...maybe there are adapters?

The chip next to the keyboard controller seems to be a 82C206 variant, that includes the RTC. Thus, the proximity of the crystal makes sense. Regarding the voltage, could be higher than that. I found one manual of a board that can use 4.5 and 6 V for the external battery. Hard to say without a manual. I'd definitely measure first which pin is positive and which one ground to get the pinout correct.

Most common external packs seemed to be 4.5V, pretty expensive and I remember replacing one with 3x AA holder

Martiini wrote on 2025-08-25, 10:58:

[...]

Thanks for replying.
Yes I have also reflected about that one. Can I somehow check if it is + on pin1 so I dont fry the motherboard?

If that's + it should feed into the RTC and you could get continuity there - but easier is to check the GND on pin 4, that should have continuity with any other GND on the board, such as the middle pins of the AT connector.

Also, 4-pin was the standard for external batteries in those days:

So you mean that JP3 is the clear cmos jumper?

I expect so.