Disconnect battery when parked?

I have a friend with a vacation house in Hawaii, he keeps an FJ cruiser there. Lots of cars get stolen in Honolulu so he wanted a way to disconnect the battery. I went to west marine and got one of these
m-Series Mini Single Circuit ON/OFF Battery Switch with Removable Knob | West Marine
And installed it on the negative side, in a hidden location. The knob is removable so you can turn it off and take the knob with you. It also keeps his battery from draining when he isn’t there for long periods of time.