I used an industrial 3.6V 280mah back up battery on a 286
motherboard to replace the oem battery. I had no problems.
If you fully charge the ni-cad pack before installing it, I would
think a couple hours on now and then would make up for the
internal losses and the power used by the CMOS chip.
On 29 Aug 00, at 3:00, Mark Willis wrote:
> Hi, all. In talking with some people about replacing Real Time / CMOS
> batteries, I have had some ideas on "Improving" these.
>
> Wanted to ask: Has anyone here soldered a Cordless Telephone battery pack
> in place, to replace the standard 3V/60R NiCad battery pack?
> (Disadvantage: It'd take "forever" to charge off the motherboard.
> Advantage: It'd run your CMOS / Real Time Clock, for a LONG time.)
>
> Just a semi-random thought, that I may try (Sometimes can get 3-AA NiCad
> packs for $2 or so, this'd be interesting for some machines that are
> normally powered off, though I may have to add a power charging circuit to
> charge this quicker when the machine's powered on!) So many machines here
> are usually off, only occasionally powered up for a few hours, and that's
> rough on CMOS batteries. I've thought of putting a 117V to 5V trickle
> charger in those machines.
>
> I am imagining a quite slow voltage-limited, current-limited trickle
> charge for these batteries (Probably just a diode from 5V then a 120 ohm
> resistor to current limit this to about 6mA so a 60mAh pack charges at
> 1/10C or so?)
>
> Has anyone reverse-engineered the charging circuit on a 386 or 486
> motherboard? I'm getting more curious on this one <G>
>
> Mark
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