Thanks for your reply and expertise Wayne.
I hope what you say about the higher temperature coefficient applies to the batteries I am using in my scenario ( high C-rating packs in F5D racing) because my prized packs are showing higher IR than I expected. I have (and tested with the IR meter this evening) six packs, all 5S 1800mAh packs connected with 4mm bullets in series from a 2S pack and a 3S pack to make 5S. Four of the packs are "older" Genesis Power 65C packs with the 3S cells leftover from another plane I flew last year and the 2S packs purchased new this spring (not optimum to mix older cells with newer, but was my only option at the time).
My other two packs are also 2S + 3S Thunderpower 1800mAh 70C which were introduced into the rotation about two months ago and are just now broken in but have been used in a race (so they should be performing optimum).
All the Genesis Power packs are right at 57 Ohms resistance with the individual cell resistance hovering around 11 - 12 Ohms for an FOM of around .59 and a max amps of .31.
The Thunderpower packs are even higher resistance with the pack being about 61 Ohms and the cells ranging from a low of around 10 to highs of around 13 Ohms for an FOM of .51 and max Amps of 28 - 29A.
I fly these packs for a race full-throttle for around 70 seconds, then throttle as necessary for landing. Average current draw during a race is about 50A and the packs typically take a nice 1100mAh to recharge.
Did I just find out there is no Santa Clause (shouldn't subject those packs to 50A)? Or, is everything okay and there is something I am missing (such as since I'm not running the packs all the way down to 20% I can use higher Amps, or batteries used for racing simply aren't going to last as long)?
So, is my world upside-down and I'm destroying my packs quickly because I'm drawing around 50A but according to the figures and the calculator they're good for only around 30A? This was in ambient summer temps (average 70 - 80F, but I did begin heating them in my car toward the end of the year when the temps started to cool).
It's odd to me that the IR of my recently better-performing TP packs have higher IR across the board than my apparently tiring Genesis Power packs.
And, maybe, without pre heating I'm damaging my packs, so heating should be part of the regimen before every flight?
Toward the end of the year it seemed as though my older Genesis Power packs were not able to hold voltage toward the end of a flight (plane slowing), but the Thunder Powers were going strong. Wonder how much of that is due to battery quality (?) and how much is simply due to cycles on the older batteries. I didn't think pulling a conservative 1100mAh at a soft 50A out of a 1800mAh 65 - 70C battery would be very much of a load.