Check your CPAP. Many operate off of direct 12 volts DC, so you connect a new dedicated cord to a cigarette lighter plug and power it direct. DOWNSIDE: CPAPS hate 15 volts, so if you go this route to save 13 watts over using the power brick, be sure to disconnect it from the lighter plug BEFORE starting the engine. They also hate voltage transients caused by starter motors. Check with the device OEM to verify.
CPAP and BiPAP internals also HATE anything but pure sine wave AC power. When I tried modified sine wave with my Respironics BiPAP my LCD operating screen tried to display Chinese or Sanscrit I don't know which. It was quickly unplugged. You need a pure sine wave (PSW) inverter. My Respironics requires 55 watts.
I chose a 300 watt quality Pure Sine Wave unit. A Samlex. There are other brands. Many will chime in here with good alternatives. It's easy to go overboard and select an inverter way too big for the amount of battery capacity you ever intend on using. Choose wisely.
