I just found out it's a 100 watt motor,
Ok, 100 watt motor at 24 volts, that will draw about 4.2 amps, however you can double that
when you start from a dead stop and accelerate with a large load (that's you). So let's say you
could draw 10 amps under large load.
As an example we'll pick 12 gauge wire which has 1.62 ohms of resistance per 1000 feet.
Let's say you have five feet of wire (2.5 ft to the motor and 2.5 ft back)
The math; 5 ft divided by 1000 ft = .005 then multiply .005 x 1.62 ohms and you get the
resistance of 5 ft of 12 gauge wire. That is .0081 ohms of resistance for 5 ft of 12 gauge wire.
Now, to calculate the voltage you will lose across your wire use ohms law.
Voltage = Current x Resistance (V=I x R) so 10 amps x .0081 ohms = .081 volts.
If you have a 24v battery you would end up with 23.919 volts after wire loss.
Some other wire resistances per 1000 ft;
#16 = 4.1 ohms
#15 = 3.25 ohms
#14 = 2.6 ohms
#13 = 2.0 ohms
You can calculate voltage drops for the others.
Note: #16 wire has a max current rating of 22 amps in open air.
But this assume 212 degree wire temp and 135 degree air temp. You don't want to run it that hot!
Oh, if you use #16 wire you lose about 0.2 volts on the wire.
Now if you use a 48 volt battery your currents will double and the voltage
drops on your wire will double.
You will however increase your horsepower by four times.
For as long as the motor lasts

For what it's worth I have a 2 hp, 28 volt motor running on 48 volts
on a gokart.
Mike