I want to use my alternator to charge an extra set of batteries which I want to connect to another motor driving the truck. can an alternator be used as dual purpose equipment like charging batteries and using it as motor to belt drive the vehicle.
using it as motor to belt drive the vehicle
Not a chance. Think about it. If you could propel a truck with a grapefruit size motor, why would we put 800lbs+ worth of engine and transmission into them?
Here's what an electric car powertrain looks like (now imagine a truck)
and this is the battery pack required to power it.
can an alternator be used as dual purpose equipment like charging batteries and using it as motor to belt drive the vehicle.
It really isn't clear what you're trying to accomplish but you can't do that with a conventional alternator. You can convert it to act as a motor but then it won't work as an alternator any more.
https://hackaday.com/2020/01/16/car-alternators-make-great-electric-motors-heres-how/
You might be able to do it but it would be highly inefficient. You would have to put a dc voltage on the rotor via the brushes to magnetize the rotor and then to introduce motion apply AC to the stater. It would have to be 3 phase AC otherwise it won't have a direction to start in. Single phase motors have a thing called a shaded pole which starts the motor in the proper direction. An alternator relies on air movement while it is turning to keep cool via internal fan blades on the rotor. The majority of heat would be dissipated when accelerating from a dead stop. It would burn up during such acceleration. The design of a motor is substantially different because of this and many other reasons.
You might look into the design of electric fork lifts or high-lows. That is a good example of a battery powered electric vehicle that's been around for years.
