The 12V cord can be plugged into any 12V outlet such as that found in a car, boat, or RV, and it can also be plugged into the 12V outlet of the Respironics battery apapter cable. We've even used the 12V cord plugged into a 3 million candlepower flashlight (which has a built-in 12V outlet on the front). At a pressure setting of 8 cm H2
O and using a fully charged battery, the run time on a REMstar Plus CPAP machine is 12 hours.
Right now, the flashlight battery option is probably the least expensive method of operating a CPAP machine from a battery. Just make sure you get a rechargeable flashlight with a 12V outlet built into it.