OK, The CH version of the Rcaxl will run on a 1 cell lipo. A single A123 I am not sure because of the lower voltage. Josey is testing that right now to see how much of the capacity it will use before starting to miss. If the voltage gets too low it will simply start missing at higher RPM's and you should land imediatly.

Bill at CH has been flying 2 planes for a couple of months now on a 1 cell Lipo. I also have been flying mine the same way. I have bench tested the setup at 10,000 rpm and it went for 2 hours 15min on a 1550 1 cell LiPo pack. Current draw was about 680 mah. The same as when it is run on a 4.8v pack at that high of an RPM. The higher the RPM, the higher the current draw. There was NO current draw increase with the lower voltage pack. On the bench I did not get a miss until the voltage was just below 3v. So the A123 should be able to run it at most of its capacity. Further testing is needed on that, but it should. The key to this EI running at that low of a voltage is not the EI itself, it is the hall sensor. The Panasonic hall sensor used by most EI builders will not run at that low of a voltage. The Allegro hall sensor the Rcaxl EI uses does. It is not supposed to go down that low either, but it does for some reason. I have tested multiple Allegro hall switches and they all seem to preform the same.