RE: Formula for determining Battery size needed
Putting aside all of the rules and general rules of thumb and inaccurate labels.
If you require an actual 125 amps then 125/C (discharge rating)= capacity (size) OR 125/capacity = "C" discharge rating
If you had a 100C pack then the size needs to be 1250 mah at a minimum. If you had a 10C pack then you need a 12500 mah pack.
If you are stuck with certain size capacity requirements of 3000-3500 mah then you need actual 36-42C packs.
I don't fly edf , but if they fly at a fairly constant power level then your desired flight time is important because that determines the minimum "C" rating and eliminate a variable.