Dennis,
The "C" factor roughly correlates to the internal resistance (R_int) of the particular cell. The higher the "C", the lower the internal resistance--at least if the "C" factor is set by the physical characteristics of the cell rather than the marketing department!

So where all this matters is in the heating of the pack during use due to the resistive heating (I²R_int--a real killer of packs.

Another thing to remember, flying at partial throttle is harder on a pack than you might suspect. For example if your throttle is set at 70% of full, then your average current "I" is being supplied only during 70% of the time. Or in other words, the peak current I_peak is actually 1/.7 (~142%) higher than the average current (I_ave)you measure. So the heat produced in the pack during the "on" time is 1.42² or~ 2 times what you would calculate from using I_ave. However the other 30% of the time the pack is supplying nothing, so when you take the average of the on and off periods, you end up with 1.42 times what you would calculate from using the I_ave for the heating calculation. So you see you may be a bit harder on the pack than you think.

But cutting through all that --are your packs hot when they come out of the plane after a flight? If they are just "warm" then I don't think you are over-abusing them due to heating.

So getting back to your first question, heating is bad, so a "real" higher C rating is better. But the other thing to remember is that most high "C" rated packs are heavier than the lower "C" rated packs (I am thinking about my 18C FMA 2100 mAHr cells and the Thunderpower Lite cells too). Sometimes it seems like if you would just buy a higher capacity but lower C rated cell, the the allowable amps out is basically the same as the lower capacity but High C cell---and both have roughly the same weight. (I haven't made any precise determination of this, it is just a feeling).

There are also issues (just look at the battery forum on RC Groups to see the controversy) about whether the super cheap packs are really capable of many cycles (since initial cost/(# flights) gives the real cost of a pack). I know that some people are measuring some of the new packs  like Hyperion and Thunderpower (both ~35C or higher and not "cheap") are capable of realistic 10C type use (a 6 minute flight) for >200 cycles before a loss of capacity is noted. Of course they are only discharged to the 80% level for each cycle.

Alan & Dean,

Happy New Year.

When I flew these packs they were only warm to the touch at the end of the flight, my guess is 110F. I think as Alan points out that because of the 70% throttle set point the amps that the pack would see was higher than the aveage. I measured the static amps at 38 and assumed the average in flight would be safely less than the 10C this might have been to close. Am using 20C packs now, on landing they are also just warm.

Best,               DennisT

Alan & Dean,

Happy New Year.

When I flew these packs they were only warm to the touch at the end of the flight, my guess is 110F. I think as Alan points out that because of the 70% throttle set point the amps that the pack would see was higher than the aveage. I measured the static amps at 38 and assumed the average in flight would be safely less than the 10C this might have been to close. Am using 20C packs now, on landing they are also just warm.

Best,               DennisT

I think battery technology has really improved since 10C cells were the state of the art---even with the cheaper cells. So hopefully we won't be seeing a lot of problems with low lifetime batteries .

But it is surprising that yours had issues--if they are just warm, I wouldn't think you are abusing them.