I'll have to agree with what else was said here.
Most 12 v ones won't live very long if you use it a lot for airing back up.
If you go with a 12v one, get the one Phong just got, it is 100% duty cycle, and can power airtools I believe without the use of a tank.
Gotta have at least 90 to 110 PSI to turn over a 1/2" impact wrench.
That's the compressor I'd go with if I did not have my Power tank.
959 kb vid with impact wrench two Octobers ago.