Well, most motherboards just use a 3 volt (3.6 for apple machines, beware) source as power for the CMOS. As long as there are points on the board, you can just solder a AA batter clip to points. I managed to desolder a battery clip fom a shitty 440zx to an old 486 machine and it worked no problems.

2015 eh? By then, when they expire, you'll be able to zip down on your hoverboard to your local corner drug store and by a plutonium based battery. 😁

I also managed to solder an old socket 7 battery clip for a CR2032 into a 486 board, it worked (unfortunately the board itself is faulty). Nevertheless the original battery was marked with 3,6V. And I have also another 486 board with a different (empty) battery that's also marked 3,6V, 60mAh. NiCd.

I'm not a specialist in this subject, hence I would like to know
- If I could use any 3V battery on those boards, disregarding the original 3,6V?
- if the electric charge (in Ah or mAh) is important, as there are modern lithium batteries available that have a capacity of 7000mAh (instead of 60mAh)?
- if any of those batteries was or is rechargeable?

Silent Loon wrote:

- If I could use any 3V battery on those boards, disregarding the original 3,6V?

- you could give it a try, since rechargeable AAs are 1.2 V compared to normal AAs which are 1.5 V and the rechargeable will work often OK (for example the GameBoy will work with two rechargeable AAs at 2.4 V even though it normaly works at 3.0 V)

Silent Loon wrote:

- if the electric charge (in Ah or mAh) is important, as there are modern lithium batteries available that have a capacity of 7000mAh (instead of 60mAh)?

- afaik its how long the battery will last, so it shouldn't be a problem. (again, for example replacement batteries for mobile phones or palmtop computers have a higher charge).

Silent Loon wrote:

- if any of those batteries was or is rechargeable?

- I think no, since motherboard manufacturers usually use the cheapest solution 😀

I desoldered a button cell clip from a mobo a while back so I could replace the soldered-on battery on an old mobo if I needed to. Those CR2032 lithium button cells are a more convenient voltage and last a very long time.

The cylindric batteries that are soldered on older boards and destroy it if not removed in time are 3x NiCd cells hence 3.6V. These boards often have a 4-pin header near that battery you could connect a 3.6V Lithium battery to, those were usually in a black plastic cuboid.

Then there are other boards with a black block labelled DS1287 or DS12887 on them. These black blocks are RTC chips with a lithium battery and crystal oscillator injection-molded on them. If it is in a socket you can replace it or with a bit of skill equip it with an own battery socket. However if they are soldered on the board you need the hot air to get it out of there...