What size power station do you need to run a CPAP for three nights of camping?
Short answer: 1,355 Wh of rated capacity — that's the ~2 kWh — large class. Three nights off-grid with no hookup. Turning the humidifier off is the single biggest saving.
The math, appliance by appliance
Appliance
Avg draw
Hours used
Energy
CPAP (no humidifier)
40 W
24 h
960 Wh
Energy needed over 72 hours
960 Wh
÷ 0.85 inverter efficiency
1,129 Wh
× 1.2 headroom (ageing, cold, overrun)
1,355 Wh
Recommended: ~2 kWh — large class. Output check: 40 W continuous, 40 W surge.
Fridges and freezers use their average cycling draw for energy and full compressor draw for the output check — that's why the numbers differ from the label.
The bare energy need is 1,129 Wh after inverter losses; the extra 20% covers battery ageing, cold weather, and outages running long. A smaller unit works on a good day — this size works on a bad one.
What about output watts, not just capacity?
These loads draw 40 W continuously with no motor surges — any unit big enough on capacity is big enough on output.
Could solar keep this running indefinitely?
Roughly 107 W of panels replaces a day's usage with ~4 hours of decent sun at real-world (75%) efficiency. Half that solar doubles your runtime instead of sustaining it.