CPAP

Check a site called cpap.com.  Back in 2016 I purchased a "DC Converter 24V 90 Watt for S9 Machines" to power my S9 ResMed CPAP unit.  The converter package included a cigarette lighter plug, the converter brick, and wires to connect the brick to the CPAP machine.  The package also provides wires with alligator clips if you want to go directly from a battery.  The unit cost $84.95 at that time.  Also check www.cpap.com/productpage/dc-conveter-for-s9-machines.html  which provides detailed information with regard to current draw at 12v DC, battery amp-hour requirements for different treatment pressures and a lot of other good information.  The unit has worked very well for me.  The 800 number for cpap.com (at least in 2016) is 800-356-5221.  I would guess they make converters for many ResMed series machines.  Good Luck.