Yep, I've had no problem hooking it up to the car's DC plug. If hes going to go this route you might want to buy a internal GPS tracker for the car, they are fairly cheap to install with a $5-10 monthly cost. Combine that with a wireless card and you have instant roadmapping where ever you go.
Its cheaper than onscreen mapping and cheaper than a road atlas with internal GPS in the car. Not to mention you have it in case the car gets stolen, you'll know right where the car is.
I went this route when I was doing discharge consultations for the hospital. Made life easier than constantly looking in maps for addresses. Might be worth it if you're son is constantly going to new addresses (like most estate agents tend to do).
