I would recommend a sullivan dynatron. It will be the last starter you buy. Expensive, but I can start up to 40cc gassers with it using a 12v garden tractor battery. I used it for many years with a gell cell 12v 7amp battery for up to .90 2-strokes. I've seen them used with a battery attached to it for easy portability. I never did that because I wanted sure fire starting power everytime. It can be upgraded with a Miller gear reduction to turn bigger engines. They are d@mn near bullit proof if you know how to take care of it (dont stay on the starter button for long periods of time when an engine wont start). Mines about 9 years old and uses the garden tractor battery in a 6-pack cooler for carrying. The ones listed are ok, but dont have the balls the dynatron does. I hate to sound like a comercial, but if you're in this hobby for the long run, this is the starter to own.
(I'm just a satisfied owner, no affiliation with sullivan)
Edwin