How to prevent Sparking when connecting batteries with an MGM controllers

[BrianG]

The resistor value is not dependant on pack capacity, but pack voltage and capacitance of your particular ESC.

The ESC capacitance will determine the resistor value. The battery voltage will determine the resistor power rating.

If you don't mind waiting between 8 and 10 seconds for the caps to charge, use a 2200 ohm 1w resistor. That will be fine for anything up to 40v battery and an ESC capacitance of 1000uF (which is pretty typical). If your battery voltage is lower, that's fine.

If there is enough interest, I can add a page to my "R/C calculations" site to assist in choosing the proper resistor and provide drawings on how to do the necessary wiring.