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How Long Will a Car Battery Run a CPAP Machine While Camping

Very Sleepy Monkey

What could be more fun than a family camping trip during the summer? Camping is good for just about everyone.  Sleep apnea need not be an impediment to enjoying a camping trip. With a little planning, there is no reason why you can’t take your CPAP machine with you.

To ensure your camping trip goes well, you just need a rock solid solution for providing your CPAP with a suitable, safe electrical supply, so you get a good night’s sleep.

The obvious solution would seem to be to hook your CPAP machine to your car battery.  Making a few assumptions, we estimate that you can run a CPAP machine for between 5 and 8 hours from a 65Ah car battery (65Ah is the average car battery capacity for the batteries fitted to the most popular cars sold in the US) and still be confident that your car will start afterwards.

That last point is vitally important. There are few things more stressful on a wild camping trip than to be stuck with a dead battery.

We detail the assumptions we have made further down in this article.  It seems to us that 5 hours is much too little time for a great night’s sleep.  Even 8 hours doesn’t allow the chance to pull the covers over and enjoy that well-earned lie-in.  With a bit of planning and ingenuity, you can certainly get away with using your car battery.  For a truly restful tent camping trip, there are better options.

Disclaimer

No one at CampingSage has medical training.  We are most definitely not qualified to provide you with advice on your sleep apnea or the feasibility of camping with sleep apnea.  Nor can we provide any guidance on the selection and use of CPAP machines.

This article is written to answer the technical question, “How long will a car battery run a CPAP machine while camping”.  The information is provided in good faith and is believed to be accurate. Decisions on whether to go camping, to take your CPAP machine, and how you power your CPAP machine `while camping are your responsibility.

If you have any doubts or concerns you should consult your medical practitioner and/or your CPAP machine provider.

Can I Take My CPAP Machine Camping?

Please do read this section in conjunction with our medical disclaimer.

The good news is, if you are one of the 22 million people in the US that suffer from sleep apnea, it is likely that it is possible to take your CPAP machine camping.  Many CPAP machines are actually powered by DC.  Their power adapters take your normal domestic AC output, and convert it to DC at the voltage required by your machine.

Many CPAP units also have car DC adapters that you can buy separately. Even if you can’t take your normal CPAP machine, there is almost certainly an option that allows you to safely do camping.

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The issue is, how best to power your CPAP machine when you are away from your normal home electricity source.

Background to Our Estimates On Car Battery Usage

If you don’t like figures and calculations, you can safely ignore the next couple of sections.  They are just showing the basis of the conclusion that a car battery is only good for powering the average CPAP for around 5 to 8 hours.

CPAP Assumptions

There are many variables in power requirements for CPAP machines. 

On average, a CPAP machine uses between 30-60 watts of power. Some, more complex machines can draw as much as 300W.  If you have a machine in the latter category, you are probably not going to be able to take it camping.

The actual power required depends on the pressure and humidity selected.  To ensure we deal with round numbers, we are going to assume a CPAP requires 48W.  This is probably on the high side for most CPAP users.

Car Battery Assumptions

On a 12V car system, 48W requires a continuous current of 4A.

In our article on powering a camping fridge from a car battery, we included a list of the most popular cars sold in the US in 2019, along with common battery capacities for each model.  The average car battery capacity is 65Ah.

Top Selling US car battery capacities.  Provided to answer the question  "How Long Will a Car Battery Run a CPAP Machine While Camping"
Top US Cars (2019) With Typical Battery Capacities

Car batteries are designed to provide lots of power, very quickly, to start the engine.  They are not designed to provide continuous, low amperage power for extended periods.  To guarantee you battery will start you car, it is recommended that they are never discharged by more than 30% capacity.  That means that an average car battery can supply around 20Ah of energy before there is a risk of your car not starting.

20Ah of capacity can provide 4A for 5hours. (4A x 5h = 20Ah). 

If we assume that the CPAP can be adjusted to draw closer to 30W (lower pressure settings require less current and power) the current drops to 2.5Amps with a possible running time of 8hours.  (2.5A x 8h = 20Ah)

How to Power Your CPAP While Camping

Car Battery

We don’t use a CPAP machine, but 5-8 hours use on a car battery doesn’t sound great.  Five hours is not a full night sleep after an active day camping.  Your CPAP is not going to stop working. Your car battery can easily run a CPAP for 20 hours or more. The problem is that you wouldn’t be able to start your car again.

So, while using your car battery is not the best way to power your CPAP device, it is a great fail-safe option.  If all else fails, you can be prepared to use your car to ensure you do get a night’s sleep.

There are 2 real options for connecting you CPAP machine to your car battery:

Car Adapter Pack and Cord

If your machine has a separate DC lead with a car adapter, you may be able to plug it into your car cigarette lighter socket.

Car leads are generally only about 5-8 feet long. That can be a major limitation. You will need to park your car so that it is almost touching your tent for the cord to reach.  Energy losses in long cables on a 12V power source means that you cannot simply attach a longer cord.

Use an Inverter. 

Inverters attach to your car battery or plug into your auxiliary output (apparently this is what I am meant to call the cigarette lighter socket).  The job of the inverter is to take the DC output from your battery and convert it to AC output at the correct voltage and frequency (110V, 60Hz).

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Typical 12V Inverter with battery clips and auxiliary socket plug

For AC at 110V and 60Hz you don’t suffer such large power losses through longer cords.  You can connect a standard power strip with long cord to the inverter.  You then simply plug your normal CPAP device power cord into the power strip.

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Typical Power Strip with Surge Protection. 15ft length provides more flexibility in connecting between car and CPAP machine

Inverters are very efficient.  You should expect to be able to power your CPAP on AC from your car battery for about the same time possible as directly connecting to your car battery DC system.

Note:  Important Technical Stuff About Inverters

Most home appliances, including laptops and TVs, are pretty tolerant of the input voltage and frequency.  In many cases, your laptop or TV power adapter converts the AC power supplied back to DC at the correct voltage anyway.

CPAP machines, like many medical appliances, are less tolerant.  They expect to be AC that is as clean and controlled as you get from your home outlet.  Domestic AC is supplied at 110V.  The alternating current follows a clean, sine wave form. Deviations from a pure sine wave are called harmonic distortion.  The total harmonic distortion (THD) of your home supply is less than 3%.  Any THD>5% could affect the correct operation of your CPAP.

Cheaper inverters produce a square wave or modified sine wave output.  Using these inverters could ultimately damage your CPAP.

When choosing an Inverter you need to choose one which provides a pure sine wave output.

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Example of a Pure Sine Wave Inverter

Pure sine wave inverters don’t have to be too expensive. Here are a couple of ads from Amazon to give you some idea of prices.

Better Options for Safely Powering Your CPAP Machine While Camping

As we have said, it is possible to power your CPAP device from your car battery. There are a few key limitations – the main one being you can’t use you Car battery for that long and still hope it will start the next day.

Luckily, there are quite a few of ‘better’ alternatives.

Electric Hookup

If you have ever used an RV, you will know that most established campgrounds provide electric hookup facilities.  All this means is that the campground provides an external power socket to which, with a hook up connector, the RV takes all of its electrical requirements

Campground Electric Hookup Point
Campground 30/50Amp Electric Hookup Point

What is less well known, is that it is possible to book a tent campsite on some camp grounds that have access to an electric hook up point.  KOA offer tent sites that include electric hook ups and other conveniences.

It may also be possible for you to book an RV pitch for you to erect your tent.  You will have to book well in advance and you may well have to provide some explanation of your medical condition.

To use a campground electric hookup point you are going to need either a 30Amp (3-pin) or 50Amp (4-pin) adapter. These are readily obtainable from most camping outlets.

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50 – 30 Amp Adapter
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30Amp male to 30Amp female hookup connector

We would generally recommend using the 50Amp hookup if you plan on using lots of appliances. Key examples include: charging deep cycle leisure batteries, running a camping fridge cooler, tent fan, and/or a tent heater. TVs, lights, computers and speakers all take power too.

On every campground, we have found the hook up point is 30 to 50 feet from the tent site. It makes sense I guess. Usually, the campground is built to cater for RVs and not tents.

That’s not a problem but you are going to need a long, heavy duty, outdoor hookup lead. Something like this from Camco will work fine.

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Camco 50’ PowerGrip Extension Cord with 30M/30F- 90 Degree Locking Adapters

Using an electrical hook up is the gold standard for powering all of your electrical devices while camping.  We have certainly done it in the past.  It can be easier getting a pitch away from the high season. 

The trouble with an electric hookup is that you are highly limited in locations you can visit and the times you can camp.

There are better, more flexible options.

Deep Cycle Leisure Battery

As we have mentioned, car batteries are not designed for sustained, low current load.  Nor should you discharge them by more than about 30% if you hope to start your car the next day.

Deep cycle batteries, in contrast, are designed to provide sustained, low current power consumption.  They are also designed to be safely discharged by up to 80% of rated capacity.  With a typical deep cycle battery having a rated capacity of 100Ah, you get up to 80Ah of useful power between charges.

There are many deep cycle batteries available. This example from Renogy is ideal

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Renogy Deep Cycle AGM Battery 12 Volt 100Ah

With 80Ah available, you can now power your CPAP for something between 20 and 32 hours without recharging.  Assuming the battery is only used to power your CPAP machine, a fully charged deep cycle battery is easily good enough for 2-3 nights camping.

If you are also running a few lights, speakers, TVs etc., the time before a recharge is required is more limited.

Deep cycle batteries are frequently used with inverters to provide AC output too. 

Options for Charging a Deep Cycle Battery

Our minimum camping stay is now 4 – 5 nights.  If you want to be camping for more than 3 nights, you must recharge your deep cycle battery.

Camping Solar Panels

The environmentally friendly source of power is solar.  Luckily, there are now many, low cost, and portable solar solutions – many have been designed for the camping market.  It is work spending a little more and looking for a 100Watt or even 120Watt panel. 

A 100Watt panel should be able to recharge a depleted deep cycle battery in about 10 hours. 

One solar panel we can heartily recommend is the Jackery SolarSaga 100W Portable Solar Panel. It’s a folding panel, so it is easier to pack in your car (cargo box for us), and produces 100W.

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Jackery Portable Solar Panel

If you have invested in the Renogy Deep Cycle Battery, you might be more comfortable with solar panels from Renogy. The Renogy 100 Watt 12 Volt panel is a great option.

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Renogy 100 Watt 12 Volt Monocrystalline Off Grid Portable Foldable Solar Panel

During the day you may have other appliances running.  If you follow our advice in other articles, you are likely to have a camping fridge or electric cooler running through the day. These will take power from your panel before it reaches your battery so charging time may be increased. 

Camping Generators

You are probably familiar with gas powered, electrical generators.  You may not be aware that there are some small, portable generators that are ideally suited to camping.

The design of basic generators hasn’t changed in decades.  Camping generators are generally, smaller, quieter versions of the emergency generator you may have linked up to your home.

The engine is used to drive an alternator which produces AC.  To provide AC at the right voltage and frequency, the engine is governed to run at a set speed – usually 3700 rpm.  Because they always run at a set rpm, generators tend to be noisy.  In low load conditions, they are also highly inefficient.

We certainly wouldn’t recommend you attempt to power your CPAP machine directly from a generator output.  Generators can be very good for recharging your deep cycle battery though.

Camping Inverter-Generators

As the name suggests, an inverter generator combines the features of both and inverter and a gas-powered generator.

We describe the inverter generator process in our article on ‘Can I Use a Generator while Camping’.  Here’s a very quick summary:

  • Engine drives alternator to generate AC output
  • AC out put is electronically rectified to DC
  • DC out put is inverted to a clean, AC output.

As the output voltage and frequency is inverted from DC, there is no need for the engine to run at a constant rpm to provide the required AC frequency.  In times of low electrical load, an inverter-generator can run at idle.  Inverter generators are very efficient in operation – a little gas can go a long way.  They are also very quiet – typically less than 52db.  That is quieter than spoken conversation and is virtually inaudible from 20 feet.

As the final stage of the inverter-generator process is to invert to AC, it is possible to get outputs with low THD (Total Harmonic Distortion).  Not all manufacturers quote THD.  However, Westinghouse claim <3%THD on their iGen series.

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Westinghouse iGen 2200 Inverter-Generator

Many other inverter generators offer similar specifications. For instance, the Rainier R2200i

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Rainier 2200i

In principle, the power output from these inverter generators should be equally as compatible as the output from a pure sine wave inverter. Just make sure you check the output is quoted as less than 3% THD.

We find inverter-generators are the clear winner in providing instant electricity in any car camping scenario. They are:

  • Light weight – typically 50 lbs or less
  • Compact – dimensions around 20x13x18 inches. You can fit it into your car camping pack up
  • Efficient – typically running for about 10 hours on a gallon of gas
  • Versatile – output available in 110V AC, 5V DC via USB sockets, 12 and/or 24V DC.

In fact, the only major downside of an inverter generator is cost. Almost all cost more than $500.

CPAP Auxiliary Battery

The final option we should consider is powering your CPAP with a purpose designed, lithium ion, auxiliary battery.  CPAP batteries seem to be designed for use with specific CPAP models only.  They are claimed to provide between 1 and 3 nights additional use. 

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Freedom CPAP Battery Standard Kit

An additional 1 to 3 nights is not generally enough for an extended camping trip.  It is going to be essential to be able to charge the battery during the day.  All of the options we discussed for charging a deep cycle battery are equally useful with a CPAP battery.

Conclusion

That’s it. It might not have felt like it but that was a gallop through just a few of the options available to power your CPAP when you go camping.

The great news is that sleep apnea does not need to interfere with your camping fun. There are many options of CPAP device available to you including purpose built, travel CPAP machines.

If you want to use your normal CPAP (and why would you really want to spend more money on a CPAP just for camping) then there are many options to ensure you can have uninterrupted us of your machine.

Answering the original question, yes, it is perfectly possible to use your car battery to power your CPAP device. It is not the best option available, and you could run the risk of not being able to start your car the next day, but it is possible.

Our preferred option would be a deep cycle battery for silent, nighttime electricity. During the day we would recharge the battery with either solar panels or an inverter-generator.

While less environmentally friendly, we opted for an inverter-generator as part of our camping kit. We find it is more reliable, easier to pack, and provides the maximum flexibility of electric power outputs.

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Keith Longmire

Keith Longmire

I’m the guy that loves camping, insists on family camping trips, and the editor and owner of Campingsage.com

I love camping and the outdoors. Through this site I hope to help you enjoy it too.