LiPo Objective Figure of Merit

There's a lot of marketing hype in the "C" rating of LiPo's.  The C-rating is the highest recommended discharge current from a cell.  Manufactures have been over estimating their C ratings for awhile.  So people have created tools addressing this issue.  One that I like normalizes the C rating using the internal resistance (IR) and cell capacity.   This tool is called the LiPo Objective Performance Calculator: LIPo Tool One wants cells that have the highest capacity with the lowest internal resistance.  Our Quadropower 4s 6200 mAhr have an average IR of 1.5 milli-ohms (really good value).  So from the web site we see:

Figure of Merit - 1.21 (the higher the better)
Max Current = 152 A or ~20 amps per motor
True C rating = 25

As the cells are cycled their IR's will increase.  When the IR = 5 they will only be able to deliver 85 amps comfortably.  This is only ~10.5 amps per motor!!!  At this point the voltage of the cells will sag very low (V = IR, right?) and we will see the low voltage warning.  We have learned that knowing the health of your battery is fairly import parameter for controlled flight.  ~mww