Backup Battery questions

I have a Resmed AS 11 and am trying to figure out what kind of backup battery to buy, mostly for the occasional overnight power failure.

Most of the dedicated CPAP travel batteries seem to be rated for about 160Wh. They make various claims of somewhere between 3-5 nights of usage without heated tube or humidifier. Maybe I'm missing something, but if I do the math, that suggests that the CPAP, by itself, only draws about 5-6 watts of power. Considering the spec sheet says the whole contraption draws 50-70 watts, that means the humidifier is using 90-95% of that. How is that possible?

Anyone with experience with these travel batteries: do they really last that long?

The other option is a portable power station. This seems like a better option as it's likely I can use some amount of humidification even on backup mode. But it costs twice as much as the travel batteries. Is it worth it?

Thanks.

The humidifier draws much more power than the machine. The S11 is more efficient than the S10, the S11 uses the same blower as the AirMini so it's probably quite low. The hose uses less than the humidifier, but likely as much or more than the machine as well. Basically its always possible to make a blower more efficient, but a heater is a heater. I have battery arrangements for both my S10 and my Z1 travel machine, I think the S10 is about 80 Watt-hours for an overnight without the heater. I don't think its practical to use the the humidifier with a reasonable size battery. As I recall when I measured it the humidifier is about 30 to 60 watts and the tube about 10 to 15 or so. I think the S10 alone is about 10 watts or so, but I don't remember exactly. Of course it also depends on the required pressure and air delivery. For portable battery operation a humidifier is not practical. The tube heat is somewhat practical but not really needed if there's no humidifier.

For what it's worth I use a power converter to make 24V for the S10 from a 20V Ryobi tool battery, of which I have quite a few, always charged. The Z1 runs directly from 12V so a portable lithium battery works, or I've used lead acid cells. It can also run from a power tool battery with a power converter. If you want to use power tool batteries just search "power wheels adapter" and the name of the power tool on Amazon, these are battery adapters that you can wire directly to an adapter or connector.