Targus has a version which has adapters both for the cigarette and the Empower ports. I use it on AA without a problem. Targus sells power tips which can be used to connect the adapter to all kinds of devices. Buy.com has very good prices on the Targus Auto/Air power adapter

http://www.us.buy.com/retail/product...9869&loc=14577

Cost is around $90. Targus will mail you one free power tip for your computer if you contact their customerservice via their web-site.