My experience is that the external battery header is a four-pin header, but with only pins 1 and 4 populated. So you take the jumper cap off and connect your external battery to those pins. One of my boards has the same setup as yours, where the ext battery header doubles as an "enable internal battery" jumper. Better understanding barrel battery charging circuit On other boards, one of the four pins is missing, and accordingly, some external batteries have a pin blocked off so that you can't connect it backward.

My 4pin connector from manual -
1. External battery positive
2. Internal battery positive
3. Connect to CMOS
4. Ground

2-3 Shorted jumper by default

…so you have found the original Shuttle HOT 409 ber 2.2 manual? I have not been able to find it in the internet. Could you share the link?

net5rac wrote on 2025-06-04, 21:06:

…so you have found the original Shuttle HOT 409 ber 2.2 manual? I have not been able to find it in the internet. Could you share the link?

No, it's a different board, but it's very similar. As mentioned above, pin 1 and pin 4 are used for the external battery, and the jumper must be removed.

Ok, I will try it out.
Thanks a lot guys!