Charge spare battery

K_and_I wrote:

mobeewan wrote:

ResMed also makes 12v DC to 24v DC converter (brick with cable that connects to CPAP) that comes with two different cables to connect between the brick and 12 volt source. One cable has battery clamps the other has a cigarette lighter plug. My medical equipment provider kept telling me that insurance didn't pay for it. At the time I had an Anthem EPO (premium) plan that provided 100% payment on medical equipment. I contacted Anthem and they said they would pay for the converter under my plan since I had 100% coverage provided I had a note from the doctor saying it was necessary. I told respiratory doctor I needed it when I went camping and he provided the note on a prescription pad for me which I turned in. Insurance paid for it. I Have used it on trips with 6 hours sleep per night for 3 nights using the humidifier. I used a spare Walmart group 27 EverStart 27DC deep cycle battery used for CPAP only. Still showed over 12 volts on the battery after I got home. So it would probably last me 4 nights at 8 hrs per night or 6 nights at 6 hrs per night.

Now there is an angle that might work. I don't think I have 100% medical device coverage, but I think I'm going to have unused Health Care Spending Account money at the end of the year. Any idea how much more efficient it is to convert from 12v DC to 24v DC instead of 12v DC to 120v AC back to 24v DC? That increased efficiency might allow us to use the humidifiers. The battery I have is a 55Ah AGM deep cycle solar power battery. So far, we have not been without plug ins for more than one night.
Again, thanks to all for responding.

I don't really know what the exact efficiencies are one versus the other, but you do lose about 10% going from DC to AC with an inverter. Then with the inverter you going back to DC at 24 volts and there's probably an efficiency loss there. With the rest Med converter you're only making one change from 12 volt to 24 volt so I would think that it would have to be more efficient overall. So far I've only used the CPAP while tent camping at a campground it did not have power and I brought my own 12 volt DC deep cycle batteries. My camping times have been limited to three nights and I've used both the inverter and then later the power adapter when i received it. I've always had power left on the battery with the inverter or the DC converter after three nights and I've used the humidifier every time. Res meds website has a PDF for using power inverters with their equipment you might take a look at it.