I have some nice gear motors that run on 12 to 24 volts, and want to use them in a medium-sized mobile robot -- maybe 30 cm * 30 cm for the base. I only expect it to run indoors, or possibly outside in nice weather. If it had a half-hour run time, that'd be fine. [If this is successful, though, I'd like to make a bigger robot that can withstand the out-of-doors, but probably only in nice weather].
I'm wondering what sort of batteries to use to power the motors. These are the choices I can see in order from what I think is best to worst.
Use one or two 12 V (lead-acid) batteries. This is sort of what I'm leaning towards, but I'm worried about how bulky and heavy it would be. A car battery would be far too large and heavy.
I already have a charger that claims to be "ideal for car, SUV, light truck, farm equipment, boat, deep-cycle, RV, motorcycle, ATV, snowmobile and lawn tractor batteries." I imagine it would charge any 12-V lead-acid battery.
Use some 9-V rechargeable batteries. They appear to typically be a little less than 9V, but it appears that there are 9V and 9.6V varieties. I would have to get a charger. These would be light, compact, but they won't last long. (230 mAH seems paltry compared to a
5 AH50 AH car battery.)
I would need to have two in series, and, I suspect, have two or even three series in parallel. That adds up to quite a few batteries and starts to negate the benefit of the small, compact batteries.
I could use 2 to 4 6-V batteries. (I didn't realize you could get rechargeable 6V batteries).
AA batteries, and lots of them. 10 to 20 1.2V NiMH batteries, though, will take a fair bit of space and mass and be take a long time to charge.
Specialty batteries (like those used in RC vehicles).
Some combination of the above -- say, two 9V batteries and a 6V battery.
Any sort of battery and a DC-to-DC adapter.
The first two options seem like my best choices. What would you recommend?