VT,

Try here:

http://batterybuddy.com/

Looks like they've discontinued the 'battery buddy' so that they can introduce the 'battery brain' for more $$$ (but still less than $70 so that's not too bad).

The only experience I've had with them was when we installed some surveillance equipment on some Suburbans for the Boarder Patrol years ago. We didn't want them to use the equipment for hours on end without the engine running and then not be able to start the Burb for the final chase.