I guess it depends on how fancy your voltmeter is.
If it's just a regular old dial gauge, the amount of energy it takes to hold that needle in place is a lot less than it takes to preserve your radio stations. I've left my truck by itself without being started for a couple months at a time, and it still started fine on it's own. Of course, I've left my headlights on before to, and had to jump myself from my auxilary battery, but that's another story.
Take care,
~Chris