some errors in the above advice, wont go into it all, but to save you blowing things up, although they do pull 12v each from 24v total supplied if equally loaded, do not lock a wheel, or something unwanted happens to the other.

I currently run...

Edgehog, 100kg, runs 2x12v 400W motors for drive, a single hawker 12v SLA battery, sidewinder controller, no problems at all.
has run 18v and 24v, without problems, but Edgehogs gearing is wrong for 24v, so it pulls too much current for my liking.
Speed at 12v is slowish but ok, 18v is good, 24v is a bit silly.

If you want any info on the sidewinder with bosch 400s Suran, drop me an email and I can give you more details about Edgehog.