I don't see the original post, so I'll just add some comments at this point in the thread.
I think most of the retail store 12V units are borderline junk, with varying degrees of reliability. Paying more for one of these doesn't mean it's a better designed unit, but more likely that it also serves as a flashlight or other feature. When looking at the internal motors and pumps in these units, one might ponder if they couldn't build a better quality air compressor/inflator with some parts thay might have laying around, such as a decent quality cordless power tool motor, a small pump, and a check valve.
Most good air compressors made for mobility are made with gasoline engines as the power source.
Real electric air compressors for automotive applications are probably limited specialty-type applications. I haven't seen any of these units in automotive supplier's stores or catalogs over the years.
Maybe the most commonly available compressors built with any quality would be the pumps made for air leveling systems in some of the bigger cars.
A number of years ago, someone posted a commercially-made mobile air compressor in the dropbox (12V or maybe 24V). It had a heavy duty motor driving a 2 cylinder, single stage air compressor pump by a belt. The switch was a HD engine starter relay, so the current demand of the motor was likely significant. There wasn't a storage vessel attached, although it could've been under the vehicle.
Another unit that I saw in an automotive painting book in the 1970s, was an improvised installation of a belt driven, 2 cylinder, single stage air compressor pump with a 12V clutch, that was fitted to the vehicle's engine. I think this installation was a project of fabricating custom brackets to mount the pump so it could be driven by adding an additional belt/pulley to the engine. This application definitely had a receiver tank mounted underneath the vehicle, and all the necessary pressure control devices in place. Taking a pressurized vessel out on highways would be unsafe, but venting the pressure before driving it would make it safe.