Noisy and messy?? Ihave a small 1000 watt generator that runs on 2 stroke gas/oil mix, just like a weedeater. Iput it in front of my truck in the parking lot and run an extension cord to the back where my charger is at, not noisy or messy at all. You can't even hardly hear it running.
Unless you're looking for some sort of miracle power source that requires little or no effort from you, I don't have any other suggestions.
You could take a bunch of car batteries and use them to charge, then recharge them at home, but lots more hassle than a generator.