I'm wondering about using 6 and/or 12V sealed lead acid burglar alarm batteries in old 'books, like the 180, Duos, 520/540 series. There are some small ones available that would suit the 520s especially, say a pair of 6V in each side in series.
I understand that the charge curves would all wrong for the onboard controller, and that I'd need to match/ limit voltages. Would I be able to take a line straight from the 24V in to a small charge control circuit, and then from the battery to the lappy via a regulator.
Any opinions? Am I likely to find/make a charger board small enough to fit, say under the trackball/between the two front battery bays?
How can I find out the battery voltage for each laptop type, bearing in mind that their existing batteries are all dead?