Hi Miguel,

You're asking two things that are hard to combine: to increase the speed you'll need a hotter motor which will draw more amps, which reduces the runtime.
Or: you add one or more cells to increase the speed, but the motor needs to be watercooled and can still burn out.

Increasing the runtime can be done by taking a more efficient motor, or using batteries with more Ah.

Greetings, Jan.