I bought a $30 plastic air compressor that plugs into the car power socket. I thought that alone made it a pain, plus it is annoyingly slow. Then I bought a metal ViAir compressor that I keep with me at all times. It has battery terminal connectors, is small, weighs about 3 pounds and is amazingly fast. I use it at autocross / track events. Models and specs are here:
http://www.viaircorp.com/compressors.html
This is a very impressive product.