Hummer H1

The Hummer H1 is basically a HMMWV built for civilian use; it has no armor or weapons fittings. However, the drive-train, frame, body, suspension, etc., are exactly the same. The H1 differs from the HMMWV in having a civilian interior, including trim, comfortable seats, stereo, and air conditioning as standard options. As a result of its commercial use, features introduced in the civilian Hummer have been incorporated into improved military versions. The H1's electrical system is 12 volts, with the two batteries wired in parallel. The HMMWV runs off a 24V system, where the two batteries are run in series to generate 24 volts.

More information:
http://en.wikipedia.org/wiki/Hummer_H1
http://en.wikipedia.org/wiki/Hummer
http://www.gmhummer.com/history/history.htm