Battery Bank total internal resistance
Resistance is easily calculated by the array size like 6S2P  =6/2 * Cell resistance as you have done.  

But good Li Ion 18650 cells might be 33 mΩ +/- 50% when fully charged and 10x this &lt; 10% SoC so when mAh is mismatched there is increasing risk and accelerated wear on the weakest cell with the lowest mAh getting charged or discharged early thus the under or overcharged resulting in higher ESR aging.  So tolerances are critical for mAh and ESR with cutoff voltage and improved lifespan with balance protection IC's.