There is an automatic shut down for boats and also made for cars. Check boaters world for the maker (I will find it if I have time). Battery power is run through it and it has a trigger wire that you would attach to a parking light or something else that is not on with the switch off. When the battery gets low it will disconnect and Waite for the key to be turned on and the hen the parking light turned on will trigger it back on. Porsche and BMW will drain their batteries just sitting for a week or so. You will loose all settings on radio and alarm.
Not worth the $79 or so in my opinion though.
Robert