I had an interesting weekend trying to figure my airplane out. It has two 4.8 volt 1300mah ni-cads that showed 5.0 volts under load. I failed the range test getting out around 125 feet with the system going into fail safe. I though maybe one of the batteries was bad so tried one at a time and the range went down to 50-100 feet. I them disconnected both batteries and tried a friends who’s battery registered 5.25 volts and it passed the range test of over 150 feet with flying colors. I would think that anything above 4.8 volts should work fine so a little perplexed at the moment.