CPAPs don't care if it is a sine or stepped wave form. Either is fine as far as the modern machines go. (ResMed says exactly that in its Battery Guide).
Now, no, car batteries are not good to use for this. They will work, but they are not built for deep discharge uses. And inverters are a terrible way to go because they are so blasted inefficient. Much better to go direct DC. But if you are due for a visit from your Aunt Irma soon, then, well, you are probably gonna have to do with what you got on hand right now. But looking at your profile where you are at in Florida, probably not.
If you have to use a battery supply, then totally ditch heated humidification. I mean, if you are in the path of a hurricane, chances are your air is pretty wet anyhow and heated humidification would be superfluous.
It would be helpful to know what your average pressure runs. Sleepyhead would be a useful tool to find that.
If we guess your average pressure is 12, about halfway between your min and max pressures, the Resmed battery guide shows it will pull 12 V current at around 1.1 amps. Multiply that by 1.5 to establish a power draw estimate with a 50% safety factor built in (in this case around 1.65 A) Assuming the battery is fully charged, you would divide its Amp Hour (Ah) rating by that 1.65 to see how many hours of used it would provide. Don't know what the Ah capacity of your truck is - it probably doesn't even list an Ah rating as it is a starting battery. Most deep cycle batteries roughly the same size as an average car battery is probably somewhere between a 50-70 Ah rating. Again, wouldn't have a clue as to what a car battery would offer in Ah. In any case, deep discharge of a starting battery is a lot harder on that battery than it would be on a deep cycle battery and may considerably shorten its life.
But being Pensacola area, you not likely be hit that hard by Irma. But you are definitely subject to hurricane hits. While you are thinking about it, it might be a good time to order ResMed's 12-24 V converter, a couple of deep cycle batteries (I like 35 Ah AGM/SLA size) and a Deltran Battery Tender smart charger to keep them charged and coindtioned. I just did a multi day measurement and determined that without heated humidification I can safely get 8 nights out of the 35 AH AGM battery with my S9 at an average pressure of 9 cm. Your mileage will vary.
in any case, an inverter is a really bad idea if you want to get the most hours out of a battery.
See
http://www.resmed.com/us/dam/documents/a...lo_eng.pdf and it will give you a good idea what to expect using your S-9 with a battery.
OMMOHY
