# Batteries for 12- to 24-V motors

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.

1. 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.

2. 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 AH 50 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.

3. I could use 2 to 4 6-V batteries. (I didn't realize you could get rechargeable 6V batteries).

4. 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.

5. Specialty batteries (like those used in RC vehicles).

6. Some combination of the above -- say, two 9V batteries and a 6V battery.

7. Any sort of battery and a DC-to-DC adapter.

The first two options seem like my best choices. What would you recommend?

If space & weight are at a premium, and you don't mind spending lots of $, then you can upgrade to LiPo (Lithium Polymer). For example, you could get four of these 3.6V 6Ah LiPo batteries, equivilent of a 14.8V 6Ah battery, and it would weigh less than 1lb, whereas a 12V 7.2Ah SLA battery would weigh around 6lbs. Of course, the LiPo's will run you about$80 versus $20 for the SLA. So as always, there's a tradeoff. Also, your numbers above are wrong...a standard (huge) car battery is closer to 50 Ah than 5 Ah. But those weigh like 40 lbs, versus the smaller 6lb one I linked above. • A car battery is 50 AH? Good heavens. – Clinton Blackmore Feb 15 '10 at 19:47 • Car batteries can kick butt. Second, NiMH is pretty standard for this, it is low cost(relatively) and will get the job done. – Kortuk Oct 25 '10 at 0:04 You can usually run motors at a lower voltage than their rating and they'll work fine, they just turn slower. So if you find a lower-voltage battery that is otherwise perfect, but not 12V, try that. On that note, I'd recommend looking into the battery packs used in R/C cars. For instance, here's a 9.6V NiMH 1500mAh battery pack for$3.99 (but currently out of stock).