I have just started to fly with only 1 1500Ma NiMH. I manufactured a "Y" conector to be able to plug both switches to the battery. After 2 11 minute flights (2 times intermediate) it takes about 680 Ma to recharge. I done 3 11 minutes flights and takes about 980 Ma, so now I only do 2 flights and recharge from my field box battery.
Also my 11' flight uses about 9-10 oz out of my 16 oz. tank.
Hope that this helps.

Rene