Guys,
Does anyone have the formulas to convert equivalent 4, 5, 6 cell pack capacities? I'd like to be able to calculate what size 5 or 6cell pack I would need to use if I were currently using say a 4 cell 3800 mah if I know the current draw and flight time.

Best,  DennisT

I use the following:

cell count * capacity / desired cell count

All else being equal, and assuming the battery manufacturer is honest, that's probably the best you can do.  It'll certainly put you in the ballpark, and you can test-fly for the rest.  Try to do better than that and you'll be dropped into a sea of variables, all of which are hard to pin down and most of which involve getting lied to by the battery vendor.  Which is why, when someone says "oh, engineering -- that's all just number crunching and no human interaction" I just laugh and laugh.