[Ryland]

closing a switch with 48v going to a motor in a vehicle that is not moving would be kind of like dropping the clutch with your car in 2nd gear and the engine revved up to about 3,000rpm, you will most likely draw over 500 amps for a second or more and if your "switch" can not handle it, it will not just melt but it will burn the contacts, creating a cloud of smoke of vaporized metals.
My 1,400 pound electric car used to have a contactor speed controller, it would rewire the battery packs for different voltages to give the full range of speeds, 48v being the fastest speed (40mph) and if you did not use the first two speeds to get moving up to at least 10mph (15-20mph was better) the full 48 volts would lunge the car forward, over the past few years I managed to snap leaf springs on the drive axle, vaporize the leads coming off the carbon motor brushes and vaporize a 3/16" by 1/2" copper bar in one of the contactors because there was a fine layer of dust on it's dime sized silver contact.

This is why solid state speed controllers are so nice, high speed switching allows for a nice smooth acceleration while keeping all of your batteries discharging at the same time giving you greater range, otherwise your range is only as good as your first bank of batteries.