A battery such as the 4000mAh 20C or the other 3s 2200mah 15C will suffice you. For an average quad, say weighing around 1.5kg, you will draw around 250watts of power on average, say 350watts at peaks. This means about 25-35 amps max. Divide that by the 4 motors and you get about 9 amps per motor at the max. Both of those batteries are capable of delivering that and so you are OK.And let me also add that the discharge rate is either given in C's (capacities) or in amps. When given a C rating, simply multiply that by the rated capacity (mAh or Ah) to get the maximum rated discharge rate of the battery in mAmps or Amps. Thus, the 4000mAh 20C battery is suppose to supply a maximum of 80amps and the 4400mAh 15C one 66amps.
Formula: (C-Rating) X (AH) = Maximum Constant Amp Draw
Now to use this formula you first need to transform your battery size from the common MilliAmpHours to AmpHours. A MilliAmp is One-Thousandth of an Amp. So here are some Examples of converting MilliAmpHours to AmpHours:
800mAH = .800AH
1350mAH = 1.350AH
2200mAH = 2.200AH
The converted number will be the “(AH)” in the formula. Now that you've your “(AH)” number, hook it up to the formula with the “C” rating number of your Battery and Calculate.
(800mAH 10C Lipo Battery): .800AH X 10C = 8Amps Max Constant
(800mAH 20C Lipo Battery): .800AH X 20C = 16Amps Max Constant
(1350mAH 15C Lipo Battery): 1.350AH X 15C = 20.25Amps Max Constant
(1350mAH 30C Lipo Battery): 1.350AH X 30C = 40.50Amps Max Constant
(2200mAH 20C Lipo Battery): 2.200AH X 20C = 44.00Amps Max Constant
(2200mAH 30C Lipo Battery): 2.200AH X 30C = 66.00Amps Max Constant
Example calculation of discharge rate:
A 3S lipo battery 5000mah pack can get you this: 5000mAh x 40C = 88.000 mAh discharge rate 88.000 mAh / 1000 = 88 Ampere constant discharge rate.
So, a 2200mAh / 40C LiPo can only handle an Ampère draw of 88A at max. So that's why the combination capacity/discharge rate is of such importance for selecting the right LiPo for you project.