[tkanarsky]

I believe most vehicle AC compressors run directly off of the serpentine belt (12v power comes from the engine anyway, why send it through the alternator and battery?) or, in the case of electric cars, off of the ~400v traction battery. The compressor draws around 1-2kW at full tilt, so in all cases it's best to run it directly off of the main power source with as few intermediate conversions as possible.

[fencepost]

Ok, I was basing this on searching for DC air conditioning compressors with results that referenced automotive and mobile uses. Possibly what I was seeing were retrofit kits?