I live and work out of a 35' long motorhome. I love it--it's the first home that I've owned. But, it's close to 26 years old and in need of a few upgrades. Currently, we've got a 12-volt battery system that keeps our water pump going and allows our water heater, fridge and furnace to light. But we can't use it to charge our computers or make toast. Eventually, we'll upgrade it's power system to include a lithium-ion battery set, rooftop solar panels and with pure Sine Wave inverter setup so that we can charge and operate everything in the RV, even when we're not connected to shore power or running the generator. For now, however, we rely on the Goal Zero Yeti 400 to help us get by. Being as I work on the road, often for weeks without being able to plug into shore power, it's an absolute essential piece of hardware.
The Yeti 400 allows me to charge all of the gadgets I use for my work. And when the time comes to replenish its store of energy, I can do so using our RV's 12-volt system when we're driving (the alternator charges it up wicked quick, plug it into an electrical socket when we're on shore power or running our gas generator or hook it up to a pair of portable solar panels for a little trickle charging.
Interested in learning more about this thing? Well, you're in luck: my full review of the battery system can be found over at Macworld.