I fly rc airplanes and I use 11.1 lipo packs and lipo chargers when fully charged a 11.1 volt lipo is 12.4 volts and they weigh on grams so you could buy you a cheap head tube pack off ebay an put them in parallel lets say you get 11.1 2200 mah packs and ran in parallel you would have 11.1 4400 mah enough to hook up to a 12v receptical and probally charge a cell phone or a lap top up for a week