No need for ignitions batteries. I have been running these units,

http://www.hobbyking.com/hobbyking/s...BEC_3A_5v.html

with a single 6V NIMH pack for the ignition and RX. So far no problems at all.

These are on smaller gassers, 20-someting CC airplanes. You have to work out how much how much the amp drain is for the whole system. Also run a "volt watcher" to see where you are on voltage drop.

Before I went ot these units I was running AAA 4-cell packs for the igntion.

I fear these engines are going to be "slimers" just like glow. Since the con rod is bused you have to run lots of oil. Thus, IMHO... negating part of the gasser advantage.