Here is an option, like the Blackberry model above, that operates on battery.
Miccus Mini-jack TX (transmitter) $35 on Amazon.com.
Operating times - Up to 7 hours playback using internal Lithium-Ion battery or continuous with USB.
2007' BMW 650i Cabriolet
| Stratus Metallic - Gray top
SMG Transmission | HUD | Logic 7 | Sport Pkg | Cold Weather Pkg
Adaptive Cruise Control | Comfort Access