I have a 120vac CPAP machine which is 15 years old. It draws 2A for the blower and 2A for the water heater. I do not have an inverter in my new Lance 1040. What make and model of CPAP machine op...
Both my wife and I have Res Med S9s. I use the optional 12 volt power connector for powering them. We have a small inverter, but using an inverter actually uses quite a bit more power. The humidifier and heated hose are both turned off when we camp. Res Med has a battery guide page for its' CPAPS. It is probably worth looking at, regardless of what brand you may choose to purchase.