The Respironics shielded DC cord system allows you to run your CPAP machine from a free-standing 12V battery.
The battery adapter cable, with its red and black clamps which hook directly to battery terminals, provides a 12V outlet. One end of the 12V cord, or cigarette lighter cord, can be plugged into the 12V outlet of the battery adapter cable while the other end is plugged into the 12V DC input port on the CPAP machine.
You can use any 12V battery with exposed battery terminals. Good choices are car batteries and deep cycle marine batteries. The 12V cord can be plugged into any 12V outlet such as that found in a car, boat, or RV. 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.