Battery operation of CPAP devices for sleep apnea treatment
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Battery Operation of CPAP Devices for Sleep Apnea Treatment, Part 2: A battery backup system for use with CPAP treatment

by Jerry Halberstadt with Gary Collins, Charles Woodson, and Lawton Mullin; and Shane Finn and others at ResMed.

A battery backup system for use with CPAP treatment


Your CPAP needs a source of electrical power. This can be the household mains, a generator, or a battery. A battery needs to be recharged after use and to maintain it in a state of full charge. This battery backup system assumes the use of 115VAC household current for recharging, although you could use a generator or even solar power.

You will need a battery, inverter, hydrometer, volt meter, distilled water, fuses, connectors, and a flashlight. In addition, you may wish to build or buy a shelf storage system on wheels so you can keep the unit out of the way and bring it into or near your bedroom for use. Also, in order to keep the battery and charger away from your bed, you may wish to use a heavy duty (to avoid power loss) extension cord from the power system to your CPAP.

Do NOT attempt to run a heated humidifier from an inverter or battery backup system.Warning against using heated humidifier

Obtaining supplies and advice

In looking for supplies and advice, a good place to start might be dealers and manufacturers serving boaters and/or recreational vehicle (RV) users, because boating and RV applications depend on deep cycle batteries. Another possibility is an automobile electrician.

Limits of this system

Due to the weight of the lead-acid battery used as a power source, this system is practical only for use in the home, in a mobile home or boat, or possibly for camping where a vehicle can be brought very close to the camp site. Because of the hazards it may not be suitable for some applications. Other battery and power technologies are too expensive for personal use. Alas, the technology is just too heavy to allow back-country hiking--unless you use a pack animal! The lightest system reported weighs in at about 10 pounds, but the majority of experience points to a package consisting of the CPAP (light ones are about 5 pounds) and a battery weighing about 20-25 pounds.


Limits of this newsletter

NOTICE This newsletter is intended for readers who have Phantom of the Night (a handbook on sleep apnea) and thus have some background in the treatment of apnea with CPAP devices. The information in this document (comprising four separate files) may not be adequate to safely construct or install a battery backup system unless you employ the services of qualified persons. This document is intended only as a basis for communicating with and employing the services of physicians and/or professionals trained in designing, constructing, and maintaining electrical backup systems.

WARNING: Unless you are an electrician with experience in battery systems, you should get the assistance and advice of a qualified person to assure that your system won't cause any safety problems or ruin your CPAP. It is most important that you confirm your information and plans with the manufacturer of your CPAP device.

This document provides information only. The reader is warned that he/she is solely responsible for any use made of this information. Making, installing, and using a battery backup system can damage CPAP equipment, or may cause personal injury, fire, or explosion. Therefore, the services of a qualified electrician should be used and safe practices should be observed at all times. The Safety Warnings are part of this document and should be read together with it. Safety Warnings

Home installation for your backup system

You may wish to rig some type of wheeled cart or shelving to store the whole system. Keep the battery on the lowest shelf for stability. You probably will not want to store the battery in your bedroom--it is not pretty and there is the problem of keeping it connected to the charging device (possibility of smells or explosion). Also, the charging device transformer creates a hum which may be annoying. Perhaps you could run a heavy-duty extension cord from the cart with the battery etc. into your bedroom during use, and store the system in a utility room when not in use.

The necessary parts and what each does

Battery maintenance:

Is the battery charged? Check both the voltage and the Specific Gravity. Final check should be a day after charging is completed. To check the specific gravity, use the hydrometer to take a reading from each cell. I found that a second reading of the same cell may produce a different value, probably because the electrolyte may not have been fully mixed until I drew some off to measure it, with a layer of water on the top. Check the battery monthly and top off the electrolyte level as needed. Follow safety instructions from the manufacturer(s)!

Charge-- Specific Gravity-- Voltage

Full---- 1.265-1.275--- 12.7

75%-- 1.225-1.235--- 12.4

50% -- 1.190-1.200--- 12.2

25% -- 1.155-1.165--- 12.1

0% -- 1.120-1.130--- ?

Measured at 26.7 C.

Battery selection:

The battery should be a lead-acid deep cycle marine/RV battery. Other battery types and power cells do not seem appropriate for such use at this time. The ampere-hour rating should be 1.5 to 2 times the power required by the CPAP for the sleeping time.

Deep cycle batteries are designed to be almost fully discharged. However, they are not designed to be subjected repeatedly to more than 50-80% discharges, and by using a battery with a fairly high rating--1.5-2 times your requirement for your application--it will last longer. Also, an older battery does not have as much reserve as a new one and thus should be originally rated at four times the power required for your purpose.

How much will it cost? WalMart sells the EverStart deep cycle marine battery, 95AH at $45 plus an additional $5.00 deposit charge for recycling. It weighs about 50 pounds. To make it easier to move the battery, consider selecting one or more batteries of about 40-60 ampere-hours. Moving 20-25 pounds at a time is much easier than 50!

Don't use a car battery except for very short times because it can be quickly ruined by being drawn down heavily; although if the battery has a high rating and you draw a small portion, you may not notice significant degradation of the battery. You can use an adapter to draw current from the cigarette lighter. This can be a practical solution if you go camping or need to take naps on a long trip. The next time you replace your car battery, consider getting a deep cycle battery which can also serve to start your car. Check with your car manufacturer to be sure that your car's electrical system is suited to this type of battery.

The logical places for information on deep cycle batteries would be manufacturers of such batteries as well as dealers and suppliers to mobile home owners and marine applications. Electricians working with automotive systems may be another source of help.

Examples of battery backup solutions

Working example by Gary Collins:

Gary lives in a location where electrical outages are common.

He leaves the charger connected to the battery and the inverter also connected to the battery. He runs the CPAP from the inverter every night. Most of the power comes from the battery charger, however in the event of a power failure the battery takes over instantly. Using the battery each night helps to prevent overcharge, and he uses the battery alone about once a week.

I don't have the info on his CPAP unit, nor do I know if he confirmed his setup with the CPAP manufacturer. I wouldn't keep both the inverter and the charger connected to the battery but Gary is an electronic engineer qualified to make his own decisions. You should find a suitably trained and experienced person to create your own system.

Working example by Charles Woodson:

Woodson has used a CPAP machine--currently, a Respironics REMSTAR CPAP with a built-in 12V power port--for over 10 years. Therefore, no inverter is needed. A standard part of his kit is a 12 DC adapter cable ($4, Radio Shack) with a plug for the cigarette lighter for use in the car.

He has used the car battery, by plugging in through the cigarette lighter, to sleep on camping trips and during rest stops on the highway.

In case of a home power outage, Woodson plans to sleep (using his CPAP) in his car with the seat tilted back.

The main concern is to avoid running his car battery down. He normally sleeps two sleep cycles of about 1:45 hours for a total of under 4 hours), and occasionally one or three cycles. His CPAP draws about 4 amps and his car battery is 50 amp/hour capacity, so 6 hours of use would draw 24 amp/hours, or about half the rated capacity; he believes he can do this and still be able to start the car. At any rate, his battery has not given him problems. [According to the information provided by others, Charles should have to replace his battery often. It would be better to have a deep cycle battery for the car if this kind of use is planned.]

Working example by Jerry Halberstadt

Designed for use only in power failures. Finally purchased AFTER the power failure of New Year's Eve which required driving at 2 AM in the rain and fog to find a motel, cost $86 and half a night's sleep. Total cost for the system itself was about $240. This backup system will be used to power a ResMed Sullivan III set to 13 cm water for 2 or even 3 nights if necessary.

A second Radio Shack Inverter will be kept in my car travel kit comprising a fully rigged Sullivan II with hoses and mask so that I can be prepared to sleep on the road or at my destination.

Working example, camping with solar power in Africa (from the FAQ)

Working example, camping with CPAP

Lawton Mullin reports that, based on measurements by and advice from an electrical engineer, he has created and tried out the setup below which he believes can provide more than one nights of operation between charges.

Although his CPAP device is fused at 4 amps, he asked a professional electrical engineer to help him. They measured the actual amperage drawn by the CPAP while running from a 12VDC battery. At full blast (with the mask off, the hose vented to the atmosphere) the unit drew 0.8 amperes, while with the mask on it drew only 0.4 amperes, all set for 6 cm. water pressure. Although Lawton does not report measuring the CPAP output (which we recommend), his many nights of testing using the battery did not result in symptoms of sleep apnea. If the unit draws 0.4 ampere for 8 hours, that is 3.2 ampere-hours per night. He should be able to get 2-3 nights, I'm not sure how many nights he ran his tests before recharging. Since he was unable to find a small deep-cycle battery, and is willing to sacrifice the battery even if it does not last for more than a few camping expeditions, he settled on an ordinary motorcycle battery. He will get a waterproof bag to protect the CPAP unit, and together the outfit weighs about 17 pounds, which would not be too much to pack by canoe. As an experienced camper he will know how to anticipate possible leaks of battery acid and make sure there is enough reserve flotation even with the extra weight.

Lawton also reports success in a one-night experiment using a 3-pound NICAD battery--the advantage is that it is sealed and thus could make up an overnight kit of less than 10 pounds!

Here's what to ask the manufacturer of your CPAP device:

I wish to make a battery operated backup system to use in the event of power failure or while camping. My CPAP device is (___________________Model) and the prescribed pressure is (____ cm water).

In order to determine the battery size, I need to know the draw in amperes of my CPAP at my pressure. How many watts does the device use? ____watts. What is the amperes usage at 115 Volts AC? At 12 VDC? ____Amperes at 115 Volts ____Amperes at 12 volts. (See Very Technical Notes, for the formula for computing the current.)

Draw in amperes at 12 volts ________ x 8 hours x 1.5 = _______ampere hours of a marine deep cycle battery suitable for one night.

If the CPAP can not accept 12VDC, then in order to convert the battery power to run the CPAP at 115VAC, I need an inverter that will not damage the CPAP.

The list of factory-approved inverters is: ____________________________________

Or, the criteria for an acceptable inverter for my unit is: _____________sinewave, ___watt continuous, _____watt peak

Will using a backup system affect my warranty? What other concerns and recommendations do you have?

How to locate and communicate with manufacturers of CPAP devices

A listing of manufacturers' web sites is included in: Sleeping on the Internet . A list of manufacturers (with contact information) is included in the handbook, Phantom of the Night.

Copyright © 1997 New Technology Publishing, Inc. Source: The Phantom Sleep Page


This document provides information only. The reader is warned that he/she is solely responsible for any use made of this information. Making, installing, and using a battery backup system can damage CPAP equipment, or may cause personal injury, fire, or explosion. Therefore, the services of a qualified electrician should be used. The Safety Warnings are part of this document and should be read together with it. Safety Warnings


The technical information which helped me create my battery back up system and this newsletter is based on correspondence with CPAP users: Gary Collins, Charles Woodson, and Lawton Mullins; and Shane Finn and others at ResMed ResMed Home Page . Their materials are used with permission. Gary lives on a mountainside and is plagued by frequent power outages. His electrical knowledge and creativity have been important inputs for this article. Charles enjoys camping and travel and is able to use his car battery while he sleeps. Lawton is determined to enjoy his canoe camping trips. I appreciate the advice and information provided to me but warn the reader not to rely solely on this information. Reference has been made to manuals of manufacturers including Schumacher, Power-to-Go, RadioShack, and EverStart, and to Phantom of the Night.

Appropriate use

The reader is responsible for any uses or interpretations made of the information provided, and is urged to obtain the services of a qualified electrician before purchasing, assembling, or installing a battery backup system.

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