I have a portable vacuum that uses 12v plug in outlet on car. Can I safely use the 12v plug in to clean my carpet with this vacuum without being heavy on the aux battery? My main concern is the auxiliary battery. Thanks. Nexus 5 ?
Especially considering the vacuum's efficience is not going to be that hot, the cleaning is going to drag on, and you know where that's going to go. I'd try to get 110 volt to the car if at all possible.
It is possible that the vacuum might blow the fuse feeding the auxiliary power socket, not to mention potentially draining the 12V auxiliary battery depending upon how long this process takes, whether the cabin lights are left on, etc. It would be much better to use a household vacuum plugged into an 120VAC power outlet.
There should be some indication of the current drawn by the vacuum. If it is of the order of ~8A or less, then using it with the car in ready mode should work OK. The 12V plug will get hot if used for long periods, but for a short suck of the foot wells, then it is fine. I use a 12V tire pump, which has similar current draw, with no problem.