Let the hive mind of Engadget get that for you.
"I am looking for a device that will stream sound from one source to several recipients. For example, I want to stream sound from my TV or stereo to my phone or MP3 player that has radio and Bluetooth capabilities. I have looked into radio transmitters and they seem like a decent choice, but I can't find one that uses external power (USB or from the plug) and I would want one with a transmit range of around 50 meters. Thanks!"
The average efficiency of running gasoline engine is ~ 20% ( http://courses.washington.edu/me341/oct22v2.htm ), and the average efficiency of idling gasoline engine is 0%, while the average efficiency of an electric engine is with enough power output that sufficient to move a car quickly should be somewhere between 90%-95% ( http://www1.eere.energy.gov/industry/bestpractices/pdfs/mc-0382.pdf ). So power losses due to transformation of energy would be offset by gasoline engine running at optimal rpms.
Also if GM used diesel engine instead of gasoline they could've achieved efficiency of ICE up to 55% ( http://en.wikipedia.org/wiki/Diesel_engine#Power_and_fuel_economy )