Does it matter if I take a 20C battery or a 25C Battery for the Bixler?
The C rating on a battery is the discharge capacity it has.
The stock Bixler motor pulls less than 20 Amps. Now this is the discharge calculation:
Big number on the battery (Amp hours) x Discharge Rating (C Rating) = Maximum Discharge capacity in Amps
The big number is the same as the amount of mAhs divided by 1000.
1 Ah = 1000 mAh
So for the 2200mAh 25 C:
......
2.2 x 25 = 55 Amps, which is well above the required 20 Amps.
For the 2200mAh 20 C:
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2.2 x 20 = 44 Amps, still well above the required 20 Amps.
For the 1300mAh 25 C:
......
1.3 x 25 = 32.5 Amps, still enough.
In the case of a 1300mAh 20 C:
......
1.3 x 20 = 26 Amps, just enough.
Note that a 1300mAh of 25 C doesn't provide the same discharge capacity as a 2200 mAh of 25 C. Even if they have the same C rating!
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For quick reference,
the mAh number (1300, 2200) is the amount of gasoline you can put in your car.
The maximum amp draw is how fast you can pull out gasoline out of it.
The Amp draw is how much gasoline your engine sucks.