ISOpwr+ - Auxiliary Battery Isolator
ISOpwr is a high powered solid-state switch. The switch turns ON whenever the car's alternator is running and turns OFF when it is not running. The switching point is 13.5 volts. The switch safely handles 40 amps and is protected with a 40 amp ATC blade fuse.
It is packaged in a small heatsink which will get warm whenever the current supplied reaches near 40 amps for a considerable length of time.