110V AC to 12V DC suggestion

[Andy A.]

A battery usually is the best answer. If you're willing to invest a little money you can buy a smaller battery that's a little easier to move around. Take a look around on McMaster for lead-acid batteries- there are a variety of options that use the same sort of non-spillable design that the official battery uses, but in smaller capacities/sizes.

The official battery has a 18amp/hr rating. Around 6 amp/hr would probably run a tethered control system and a few small motors for quite some time while being considerably smaller/lighter. Expect to spend somewhere around 30-50 dollars.

You can charge the small batteries using the same chargers you use for the big batteries as long as you can limit the charge rate- 1amp would be the safe limit for most cases. Smaller batteries also have lower safe discharge rates, so trying to run a full size robot could overheat and damage it- so don't do that!