Need some help here. Going camping and got a sleep apnea machine couple months ago, which I am totally dependable to it. Trying to figure out if it would drain my oem battery if I use the machine with the 4runner inverter for 6 hours.

This is the manufacture specification:

AC Input Range - 90W Power Supply: 100 - 240V, 50 - 60Hz, 1.0 - 1.5A

I've been trying to figure it out myself, but it has been a roller-coaster.

Thanks in advance.

Hi Payara

The standard car starter battery is designed to provide short bursts of very high current but not long steady drains of low current. Also, to run the 4Runner's inverter the key has to be on so there would be extra battery drain without the engine running. I don't think you could go 6 hours.

Would the CPAP be used only one night or for multiple days/nights?

If you could measure the CPAP machine's power consumption that would be great. The numbers you posted may be the max limits of the supply but not what the CPAP actually consumes when running.

The Kill-A-Watt is a good way to measure the watts consumed in 6 hours,



https://www.amazon.com/P3-P4400-Elec...sr=1-2-catcorr



Try to measure the CPAP machine and a solution can be designed to fit. Maybe someone else on the forum has the CPAP numbers and can chime in

The OEM battery is not designed for this kind of use. The 4runner inverter located in the trunk is also not an always-on inverter. You would need to keep your car on the entire duration of the 6 hours. You should invest in a high quality portable power supply if your life depends on it.

have you checked if your cpap has a travel kit, i know some have lithium battery kits you can get (although they are probably way overpriced if you have to pay out of pocket)

if you do need to use a battery, what is the output of that 90W power adapter? assuming it's DC you can get a DC-DC power adapter which will avoid the efficiency losses of an inverter.

i doubt your cpap is using a constant 90W, @teotwaki 's suggestion to check the actual power is a good one or if you google the model maybe you'll luck out and someone else has already done that. from a quick google it looks like the non-heated models are in the 30-60W range?

your stock battery won't be good at this, it's not made to cycle and you would kill it quickly even if the wattage is low enough that you would technically have the capacity. you will need to either upgrade your starter battery, get a dual battery, or get a standalone battery. there are pro's and con's to each solution, and your budget will also play a big roll in that decision

You could always lug around a deep-cycle battery and run a power inverter off that to power your CPAP. If you are mechanically inclined, you could even run it as a second battery so your truck charges it while driving.

Much more efficient to buy a 12v cord that fits many newer cpaps...as long as you have the battery to run it.

Check with your local supplier (or on line) to see what your machine would need

I will install a dual battery system, but not for this trip. One of my friends have a dual battery system on his runner. I've used it once on my 4runner, kept the motor running for 5 hours (it was to hot outside and wanted the AC on).

So, how to know with a 12v adapter how much would the battery last?

BTW, amazon sells the adapter but you need a Business account and a Healthcare license.......

If it takes 1 amp on an inverter, the inverter will use 10 amps from a 12 volt battery. Won't be long until the battery is too low to start the 4Runner or run the CPAP. It's close to a 10:1 ratio to get from 12v to 120v.

Small, quiet portable inverter generator may be needed.

Sounds about right to me…

1 amp x 120 volts AC = 120 watts
120 watts / 12 volts DC = 10 amps
Efficiency 10% loss = 11 amps on the DC side per hour

Generally speaking, it’s a lot better to talk about power consumption in watt hours rather than amp hours… at least when you are working with conversions and different voltages.

If your machine uses 1000 watts over the course of 6 hours using 120VAC, then here is how you can convert it to DC. Also don’t forget to account for the efficiency loss of the inverter in the DC to AC conversion.

1000 watts / 12 volts = 84 amp hours
Inverter efficiency loss, estimate 10% (check the spec sheet), 84 x 1.1 = 92 amp hours

Deep cycle battery that is advertised to have 100 amp hours is about 50 amp hours usable, should not be discharged more than 50%, so really you would need two to accommodate a 6 hour run time.

Not two weeks ago I sat through a "training" course on lithium batteries and standalone battery/inverter packs that were designed with cpap machines in mind. Right now I couldn't tell you their name if my life depended on it. I'll see if I can find the info when I stop by the shop tomorrow.


Yup. Once the voltage drops below a certain point the inverter will shut itself down.

Mmmmm...going to disagree. Deep cycles are designed to be discharged and recharged, as long as they aren't left discharged for any appreciable length of time, and/or constantly recharged at a high rate.

I've built a lot of different battery systems over the years, but I only mentioned that as a general lead acid rule of thumb... you can absolutely discharge it lower, but you will see some degradation in service live over the course of time.

Its fine if you need to do it occasionally, but cycling it regularly, like in a solar setup , a 50% DOD will yield you a longer service life than something being pushed into the 70% DOD level.

I have a lithium battery bank for a solar array, and while depth of discharge there matters too, you can go much deeper without service life problems. Much more usable capacity.

No one can tell you how long it will last with the information you provided, without knowing the actual wattage it's all just a guess

I've been in the RV industry for 25 or so years, flat dead deep cycles are an everyday occurrence. Lead acids are fairly robust, depending on your expectations. It's also pretty common to replace them every 2-3 years, even when they're maintained.

I fully agree with you on solar. You need to be mindful of your power consumption or you're going to eat batteries in a hurry.

Lithium is pretty awesome. Expensive out of the gate, but over time, not so much. Run time is way better. We're gearing up to see them more and more in the RV industry...I just hope they've skewed the designs to be well beyond idiot proof. I expect to see a lot of ruined $400 batteries.

With the info they gave we can at least formulate a worst case scenario...

Thanks guys for all the help!

After going back and forward found a cpap 12 volt converter, based on customers reviews it will run 6+ hours without any issues. It's $100 but I think is the way to go.

Thanks again.

Personally, I'd go for a bit longer run time to give me some wiggle room.