Found this voltage stepup unit for sale in Hobby city. Done some tests and it supplies about 5v to a max of 1.5amps. I tested it to work down to 2.75v.with my rcexl system. With a single A123 rated at 3.3volts, a 2300mah batt would work very well powering an ignition unit safely and with minimal weight. I tried and and found the spark to be good even at minimum voltage.
I'll run some tests but so far I'm quite happy with the results.Finally a quick recharge at the field without worry.