It disconnects the battery from the alt so it doesnt drain the alt as much.
http://www.ehow.com/how-does_5005295...tor-work_.html
It would power your devices for a short period of time, and not very well seeing as they wouldn't receive full voltage.
I'm not sure where this message got lost but if you plan on spending a zillion dollars on making a grand prix fast adding another 40 pound battery is not a good idea.
If you have money to burn on your car you have money to burn for gas.