The CH is one of the best ignitions ever made and they will handle 6v, or more accurately 7.2v on a fresh charge for quite some time, but not forever. Unfortunately you cannot get another CH anymore so you might want to consider using it at the voltage they rated it at. There was a reason for that rating, and the reason is heat. Excess voltage is disposed of as heat. Heat is and always has been the enemy of electronics. Things don't happen over noght but eventually that ignition, run on 6v, is going to crap out on you. I know from a whole lot of personal experience the CH can last a few THOUSAND hours of running time if used at the rated voltage. Bill from CH posted some current draw numbers for their ignitions some time back. It was interesting to note how much more current was consumed at 6v over 4.8.

So yes, you can run it at 6v+. If I had to make a choice of running a $150.00, top of the line ignition at 6v to save buying an $18.00-$25.00 battery or run it at 4.8v and keep it forever my choice would be simple. I might run it one weekend at 6v but by the next I'd have a better battery for it. But that's just me. I've used hundreds of their ignitions and know how reliable they can be, and also know how to shorten their lifespan by a considerable amount.