Actually, you don't always save weight by going to a lower battery pack! There are two reasons, both to do with those inflammable numbers . First, motor power in watts is determined by one of Ohm's laws; power = volts x amps. That means that if you needed a 4,000W motor, one that ran at 5S (18.5V) would draw 216A, while a motor designed for 10S (37V) would only draw 108A. In both cases, the motors have the same output and require the same amount of energy to run for three minutes.

Next, batteries store energy and its measured in watt-hours. The watt-hour capacity is calculated by voltage x amp-hours (like that last formula, with time included). That means an 18.5V, 4AH pack has the same watt-hour capacity as a 37V, 2AH pack. If the packs were both from the same manufacturer, they would probably weigh almost the same.

Putting those facts together, it means the lower voltage 4KW motor needs the same weight of batteries as the high voltage motor to run for 3 minutes - there is no weight saving in the battery itself. There are some other factors that affect the total weight and cost; the lower voltage system is drawing twice the current and requires thicker, heavier cables, connectors and removable links. Its also harder and more expensive to make a high current ESC compared to a high voltage ESC. This is why large RC plane motors are mostly low KV and high voltage - its just easier and cheaper for the manufacturers to do it that way.

The only real reason to stay with low voltage is if you want to power the drive motors off the same pack as the weapon motor. That has the simplest wiring but runs into the high current issue above. To get around that, you can run completely separate packs for the drive and weapon, or run a split voltage system where each drive motor runs off one pack while the weapon runs off both packs and twice the voltage.

Bottom line: Ohm was a mean bastard out to ruin our fun!