5? Okay. When the car engine is running, it makes a shaft of metal spin. That spin is used in two ways. The spinning shaft pokes out the front and the back of the engine. Typically the part sticking out the front of the engine will have a belt attached to it and that belt wraps around all sorts of other devices that use that moving belt for mechanical power. One of those devices is an alternator, a miniature electrical generator. Electricity is generated as long as the engine is running and the belt is spinning the alternator.
That spinning shaft also pokes out the back of the engine, where it goes through a series of gears known as a “transmission” which in turn spins the drive shaft which spins the rear wheels.
What they’ve done here is attach an alternator to the drive shaft. This means it will only generate power when the vehicle is actually rolling, not when idling at a stop light or whatever. Hopefully this is some kind of auxiliary alternator for extra power but I’m having a hard time guessing the purpose. If you need more power, you get a bigger alternator, you don’t sprinkle additional ones throughout the chassis.