5C battery charging?! I don’t even do that with my drone batteries during a race - maybe 2-3C. But if I have time 1C is the way to go for longer battery life.
Watthours just makes a good comparison between packs that have different voltages. If I swapped out to the higher voltage battery I’m building 12s to 14S, the current draw would be less (if I was going the same speed).
For 6S batteries you have 4 total right? When you take 2 batteries and put it in series you get a 12s(cells in series) (50.4V max and 44.4 average voltage). Your amp-hour stays the same at 10Ah. Watthour is 44.4V * 10Ah= 444Wh
When you take your set of 2 batteries and put another 2 in parallel you are at 12S still but your amp-hour is 20Ah. Watthour is 44.4V * 20Ah = 888Wh
For the C rating for charge and discharge - I wouldn’t go with the label especially for the peak- most are overrated and will degrade the battery over time. But for 20Ah battery pack with 12c that is 240 (20Ah * 12c), which you shouldn’t get anywhere near (maybe 100-150A trying to get on foil).
For charging at 5C if you split all your packs back into 6s. 40A charge from 5C * 4 battery. Or 160A charging or about 3550W (6cells * 3.7V * 40A * 4 batteries) of power going into the batteries. If you had a charger, you’ll need to hook up to a 240V outlet because most 120V outlets can do ~1500W max for the whole circuit (or charge on a couple circuits). I’ve popped a breaker charging my efoil battery on the same circuit as my running 3d printer. (was charging at like 1300W).
Anyways long mathy post My 35AH 12S battery (1554Wh) battery gives me about 45 minutes of efoiling (going about 10 miles). I would expect you to get ~30minutes?