RE: LiFe Batteries
A123s are a different animal completely, don't go by the voltage alone, the nominal Voltage is 6.6 or 3.3 per cell. and they will hold at 6.7-6.8 for the whole charge, then fall off fast.
What you need to do with them is charge, fly a complete flight or 2, and then recharge, then calculate how many Milliamps you had to put back into the pack for X amount of flight time,, then you can figure your flight time per charge cycle.
Good luck,, I love mine