I feel your pain; snarling wires all over my car's interior drive me nuts. But charging batteries in your car doesn't strike me as very elegant. You would be going from DC to AC to DC again in this scenario, with inefficiency at each conversion. However, if you really want to do this, the device you want is called an inverter, not a converter. Look for one made by a company such as Tripplite, which has a lot of experience in things like this. It makes a wide range of inverters. You might also keep an eye open for the coming breed of in-car inductive charging pads, such as these examples from Splashpower and Edison-GE. Or, if you're in the market for a new pickup, consider a GMC Sierra Hybrid with a built-in 120V AC system.