I'd say no, there are still too many things that can't be turned off.  I had an alternator go out on my Chevy Blazer on the mail route a couple winters back.   Stuck a new battery in and I was almost done with the route and had a 30 minute drive home.   So engine ran 40 minutes and two starts and battery was dead enough when I got home that it wouldn't start.   Had heater fan on low and shut off everything else including headlights.