I also own a Double Four and use it for off-grid applications, like camping, bluegrass festivals, and busking. I've used it primarily with an NS design upright stick bass (NS-CRM) for bluegrass, but also have used it with conventional electric bass camping, as well as a small PA when hooked up to my iPod. Good sound. Not going to level any small buildings or replace your regular amp, but ideal for what I was using it for. Echo what the other reviewer said about the laptop battery being an ideal power source. The Double Four, Battery, and chords all fit within a standard-sized student backpack, that I carried it on a Southwest Flight with no problems and no questions asked.
Phil Jones Double Four BG-75
Very small, light, and powerful hi-fi bass amp that can be used with a battery outdoors.