I've been using a CPAP in a tent for years, powered with a battery. My main CPAP is a now-older Philips Respironics RemStar with a humidifier. The humidifier is the main load on the battery. Current consumption varies a lot depending mostly on the humidifier setting, from about 3 Ah/night with no humidification to as high as 15 or 16 Ah with maximum humidification from a 12 volt nominal battery. I initially used a conventional Li-ion battery sold for the purpose. It was three cells so a bit under 12 volts but ran the CPAP ok. Then I got concerned about the (remote) possibility of a flaming battery failure in flight and switched to using LiFePO4 type batteries. They weigh just a little bit more but are considerably safer. They're also considerably more expensive, though. A 20 Ah battery was large enough to reliably operate for one night under any conditions, and at fly-ins like Clinton or Oshkosh I could recharge each day. I found that at Clinton I could get by most of the time without running the humidifier, so the battery would last quite a bit longer. But unless the relative humidity is very high like it was a Clinton, I can't tolerate using a CPAP without a humidifier.

Then I discovered this CPAP [cpap.com]. It's expensive but has two major advantages: First, it's a whole lot smaller and lighter. Second, it has an ingenious humidification system that uses a lightweight waterless cartridge in the hose that somehow captures the water vapor in exhaled air and uses it to humidify the inhaled air. It works very well. Without a heated humidifier, the power consumption is much less than the standard CPAP. Unfortunately, it requires 24 volts so I bought and use the optional high efficiency voltage converter which weighs just a few more ounces. Although you can use a 24 volt battery directly, operation from 12 volts nominal provides a lot more flexibility for batteries and charging. Consumption is a little over 3 Ah/night from a 12 volt battery so a 10 Ah battery will run it for about three nights -- enough for most overnight fly-ins -- without recharging. I use the small CPAP for all traveling because of its small size and weight. I've also insisted on using distilled water in my main CPAP so the small one also eliminates the need to carry and/or obtain distilled water.

At Clinton I just charged the battery during the day in the FBO. On my first time at Oshkosh I used the charging station near the showers. The problem with that was having to stick around for several hours and babysit -- those batteries are expensive and, although there's very little risk of an unattended one being taken, I'd be without a CPAP for the rest of the time if it was. So when I went to Oshkosh a second time -- with my small CPAP -- I brought along a 50 watt foldable solar panel and put it on top of the airplane, running wires inside through the seal and solar charging the battery during the day. I was there for nearly a week and each day recharged the 10 Ah CPAP battery, my son's and my computers, a small lantern, a cell phone power bank, and various other gadgets each day without a single trip to the charging station. We charged our cell phones from the power bank at night. I could have gotten by with a smaller battery for the CPAP, but the extra capacity would have allowed us to run for a couple of extra days without direct sun if it clouded up (which it didn't, except briefly) and to recharge cell phones and the like.

Send me a PM if you'd like any more details.

Roy

States where I've landed my 150
[Linked Image from eznec.com]