Hi Piper,
I have a lighter socket adapter for the MRX but I have not tried it yet, I think I will stick to batteries for now.
The MRX runs on 2x AA batteries, so I'm just using some regular Energizer NiMH rechargeables and will carry a second pair in my flight bag and change batteries as needed between legs on longer trips.
It seems to work for about 4.5hrs+ before needing new batteries.
I imagine the power draw on the XRX would be higher though. Have you seen these?
Zaon Flight Systems - All