Running tire inflator directly off the 12V

That's what I would do, or at the jumping points under the hood.

 

Jump point under the hood would be the best/easiest. I wouldn't put the car in "ready" though. The pump could generate spikes on the 12V system. As long as you don't run it for more than 30 min. it shouldn't drain the battery much.

 

If you attach it directly to the car battery, you have voltage. No need to start the car unless you'll draw so much power that you think you'll deplete the battery, which a tire inflator isn't going to do unless you're inflating a whole lot of tires.

Of the inflator's designed to connect straight to a car battery, it should have a fuse.

 

I just blew my lighter socket fuse doing this. My little compressor draws a ~30A surge for ~1S on startup, then 18A while running. Hasn't been a problem for any other car, where the sockets are usually fused at 20A, but in the Prius they're fused at 15. Oops. And they're those miserable low-profile fuses which are just starting to trickle into stores.

So. "Powerpole accessory connector straight to the battery" has been on my car ToDo list for a few weeks, guess it gets bumped up to high priority. One in the rear, one in the front? Le sigh. Got some nice Airpax DC breakers for the project, though, so I won't have to replace anything next time stupidity happens.

 

You don't need to connect physically to the battery. There's a connector block under the hood, near the fuse box, which has a direct 12V from the battery. This is easier and safer (no chance of a spark igniting hydrogen gas).

 

At 18 amps, that product is abusing the socket, which was not originally designed for such currents.

 

Rule 1: start the pump before connecting the pump to the tire.

The back-pressure from even a partially inflated tire increases the pump starting current by a huge amount.

**mod note - merged and fixed quotes**