How do I prepare for an interview with my Battalion CSM to become his new driver and what should I expect?

A lot of folks have offered a lot of good advice. What I'll add is don't be too upset if you don't get the gig.

A driver (like a flag aide) is a pretty personal thing... You see 'sides' of your boss that subordinates usually don't get to see-- hopefully not literally, but you never can be sure he won't have to change- clothes on-the-go...
A whole lot of the 'selection process' for a job like that is about chemistry and you can't fake that. You can't study for it, you can't increase or decrease it. It just is what it is.
Likewise if you do get the gig and later get 'fired' for apparently no reason-- it is chemistry. Don't take it to heart.

be honest in your answers - CSM's can smell bovine fecal matter from kliks away. Don't sweat it troop. be truthful and keep his vehicle squared away, and you'll do fine.

You drive careful.