The Anker PowerHouse, a compact 400Wh / 120Ah Portable Power Supply is available on Amazon for $329.99 & FREE shipping in the US. Cheapest ever!
Great solution for camping or as an emergency backup.
Basically, it's a rechargeable power source with silent DC/AC Power Inverter, with 12V Car, AC & USB outputs for powering & charging many types of devices on the go.