RE: Ignition battery
I had an issue with a Falkon ignition and a "standard" 4-cell NiMH pack. The impedance on these are relatively high and caused erratic running of the engine after a few minutes. Switched to a NiCad and the problem disappeared. Subsequent testing with a low impedance NiMH did not exhibit the same problem. Capacity is not the whole story with NiMH. Impedance is critical, especially where a large number of hi-powered digitals are in use. This is IMHO, why some servos are rated for NiCad use only.
Safe Flying!