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I recently had a PM concerning picking the proper battery for camping and choosing between flooded and AGM style batteries. I wanted to collect a few thoughts in one place.

If you just want the description of my recommended system:
viewtopic.php?p=1129137#p1129137

If you're looking for how much power you use, a start is my summary of usage:
viewtopic.php?p=1130596#p1130596
The result was 4 Amp-hours a day, but my pump (Philips 560) is fairly efficient, and my pressure of 9.5 is modest, so your needs might be higher. In general, the range will be between 3 and 8 AH a day, with about 5 AH being typical. BTW, high altitude also increases the power use.

Humidity and heated hoses are very costly. I measured up to 18 AH a day, and I never used a high setting, which could bring it up over 30 AH. Unless you're camping in a desert, or other dry climate, I strongly consider leaving the humidifier home. Note that I did find a setting that kept humidifier usage down to 4-5 AH while providing some relief.

Inverters are very handy gadgets but they are very inefficient. Although they all advertise "90% Efficiency" that is only at certain outputs; in practice they are actually about 60% efficient. This means that a battery that could go 5 nights with a direct 12V feed, will only last 3 nights with an inverter. Philips, and other companies, have a DC power cord for $25-30 that is 100% efficient. ResMed uses 24V and a proprietary plug, so their solution is a $85 DC/DC converter that seems to be over 90% efficient.

Now for the batteries. I want to focus on lead-acid batteries, but first a word on lithium packs. The price on these packs has been going down steadily, so perhaps in a few years all the traditional batteries will be obsolete. But for now, their use for cpaps is still limited by capacity - most are about 8 AH - and cost, roughly 5 to 10 times the cost of traditional batteries. Most are designed for cell phone and tablet charging and aren't really setup for cpaps; those that are tend to be pricey. They do offer light weight, so they may be the only good solution for some applications, and for one night they are certainly a reasonable choice.

Lead-acid batteries have been around for over 160 years and all use the same chemistry, but there are significant differences in design and packaging. Most important is that car (starting) batteries are designed for a short burst of high power, followed by an immediate recharge. If used in this mode, they will last 5 years or more, with thousands of these starting cycles. But if they are fully discharged, their life will be only a few dozen cycles. Batteries tend to wear down, so if an older starting battery is used for a night for a cpap, it might not be able to start the car in the morning. Of course, this is especially true if humidity is used. This is essentially the same as leaving a car door open so the light stays on all night. If you plan on sleeping in the car, a good solution is to bring a second, deep cycle, battery which is charged up while driving, and then used to power the cpap at night.

Deep cycle batteries are designed for long slow discharge, and are commonly used in golf carts, floor buffers, RVs, and boats. In this and other forums, they are often referred to as "marine batteries" but you should check for "deep cycle" because some marine batteries are actually starting batteries. (I have two marine starting batteries on my boat, along with four deep cycle golf cart batteries.) Deep cycle batteries will be good for hundreds of deep discharges. However, the exact number of cycles you get will depend on how deeply they are discharged - if only discharged 50% they should last a thousand cycles or more. But 80% will mean several hundred, and this might be OK if you only need it for a few weekends a year. Running a battery down completely is always bad, so this should always be avoided.

There are a variety of types of lead acid batteries, but the two we'll look at are Flooded Maintenance-Free and AGM (Absorbent Glass Mat) batteries. The basic difference is that flooded batteries have liquid acid, somewhat diluted but still very corrosive, while in AGM batteries the acid is contained in a paste and effectively sealed in the battery. Newer flooded batteries are called "maintenance free" but they are not completely spill proof, nor are they actually maintenance free, but they are designed so that with normal use they don't vent much gas so you won't have to add water, and they can be gently moved around without spilling. AGM batteries were designed for fighter planes and can be run upside down. Unless they are severely overcharged, they will not vent any gas.

The cost of AGM batteries has gone down in the last few years, so they are definitely my first recommendation. They are almost all deep cycle, and are commonly found in uninterruptible power supplies (UPS), jump starters, and mobility scooters. In particular, the "U1" size AGM batteries (24 lb, 35 Amp-hours) found in mobility scooters are frequently sold at $65 are a good choice for in house backup and several nights of camping. If your use is 5 AH a night, one of these should go 5 nights with a fair margin. Even having two is probably better than one larger battery, since they'll be easier to carry around. If you want a larger AGM, 100 AH batteries can be found for about $160:
https://www.amazon.com/100Ah-SOLAR-WIND ... 100+ah+agm

If you're looking to save money, you can get a WalMart flooded maintenance free marine battery starting at about $75 but they'll ask for an old battery in trade (core exchange). Make sure they say "Deep Cycle" as the "Marine Starting" versions look almost the same. The power is 80 to 110 AH, proportional to the weight. This might be the best solution for some folks, but I have trouble recommending them for any application that implies having them next to a bed, or carrying them around, or even sitting in a trunk.

On charging: the charging of AGMs and traditional batteries is almost the same and many chargers have setting for both. I recommend "BatteryTender" brand chargers as they have a long reputation of gentle, safe charging. However, even the largest is only 5 Amps, so they are not designed to quickly charge a large battery. I keep a larger Shumacher charger for dealing with car batteries. Regardless of type, no lead acid battery can be fully charged in a short time, they take many hours to go from 85% up to 100%. Its possible to charge a camping battery from a car, either with jumper cables and "fast idling" or a cable designed to plug into the cigarette lighter socket. (Sockets are often fused at 10 to 20 Amps, so this method shouldn't be used with large, deeply discharged batteries.) 30 minutes to an hour will not "top off" a deeply discharged battery, but it can certainly put a lot of juice in. The common protocol for boaters is for daily discharge to about 50% and then charge for an hour or so up to 85%.

A few more points: all of these batteries will discharge at a very high rate if the are shorted out. I have some melted screwdrivers to prove this! It is best to keep them in a battery box, or at least have battery terminal boots. The output should be fused. There are boxes like the MinnKota box with fuses and 12V sockets built in (about $60). BatteryTender chargers come with most of the cabling needed for a "plug and play" solution; refer to this thread for some details:
viewtopic.php?t=102775
[Edit: this post is duplicated below]

Enough for now. I'll more info on other topics such as lithium options and solar charging later.

This thread needs to be stickied.
Thank you, CapnLoki, for your hard work and generosity in sharing what you have learned.

Every few weeks there's a query that goes like "I have a CPAP. What kind of battery should I get?" Unfortunately there is no simple answer because the choice has to be customized to the need. Here's a few scenarios to help focus in on a situation.

"The power where I live frequently goes out for a few minutes." In this case you can get by with an Uninterruptible Power Supply or UPS. These are designed to run a computer for about 30 minutes so that files can be saved and disks spun down. I have an APS 550 for this purpose; this is a very typical unit that can be had for under $100. It has a 7 AH AGM battery, charger and inverter built into a sturdy package. Factoring in the inverter, the net output is about 4 Amp-hours, so this might be enough to go much of the night, but if humidity is left on, it might be good for only an hour or so. So the UPS is handy, but certainly doesn't work for camping. BTW, many UPS units have an annoying alarm when the power goes out. If this is not wanted, it can usually be turned off with a computer configuration.

"Can I use my Jump Starter as a UPS?" Yes. My issue with these devices is that the generally combine cheaply made components with a modest size battery, often 18-20AH. The "all in one" package may work for some, but as we'll see, you can get more bang for the buck with other approaches.

Now we'll move on to longer time frames. But first, a word about humidity. In every discussion of battery powered CPAPs, you’ll see a phrase like “assuming you don’t use the humidifier.” So what gives? Are we not allowed to use humidification with a CPAP? The answer is simple: using humidity will at the least, double the power used, and can easily increase it by a factor of 4 or more. The heated hose is also very power consuming. Fortunately, when battery power is needed, the need for added humidity is often reduced: many camping locations are humid; when there's a power outage the A/C won't be running, etc. If on the other hand, if you're camping in Palm Springs, you may still need some humidity. My advice is to use the lowest setting and know that the power use will be about double. Otherwise, you'll need a very large battery. My assumption for the following is that no humidity or heated hose is used, except where a UPS is used.

"Sometimes I lose power for a day or two. How can I be prepared?" This situation is at the heart of my recommendation for an AGM U1 battery. This is a mobility scooter battery, cost is about $65, weight is a luggable 24 pounds and power is 35 Amp hours. Even with a good safety margin this is enough to go one night with humidity (assuming it isn't a worst case) or several nights without. The AGM battery is safe in the bedroom (think of all the elderly folks with two of these in their scooter) and can be easily maintained by a small charger. Cost is between $100 and $150; assembly is two bolts for the the battery terminals. Details of this type of system can be found in this thread:
viewtopic.php?t=102775

"Can I use the scooter battery system as a UPS?" Yes, in the setup I show a 1 to 5 splitter on the battery - one output goes to the CPAP, another can go to the charger. (Others can be used to charge cell phones, etc) With both the charger and CPAP connected you essentially have a UPS. Much of the power for the CPAP will come from the charger, with any deficit made up by the battery. During the day the battery will get charged up. I don't recommend using this all the time because its means cycling the battery and charger every day; I save this for nights when storms are predicted.

"I want to be prepared for the Big One!" The scooter battery system is generally good for several nights, but if you're concerned about long outages, a week or more, you can get larger batteries. A 100 Amp-hour battery cost abour $80 for a basic flooded, or $160 for an AGM. They can be kept separate or wired together into a large bank so solutions for several weeks or more can be put together. The care and feeding of such a large system is bit beyond this post, but I will add that whole house generators are the solution picked by some who live in areas where the grid can go down for more than a couple of days.

An now for some more mobile solutions:
"I'm driving across the country and plan to sleep in the car. Can I just plug in to the cigarette lighter?" Running from a car battery is never a good idea. The starting battery is designed for a short burst to start the car, followed by a complete recharge. Deep discharges can lower the voltage to the point where starting is iffy. This of course is worse if the battery is old, or small, or the car is hard to start. In general its much better to get a second deep cycle battery, charge it from the car while driving and then use it to power the CPAP. The scooter battery mentioned above is good choice for this - 2-3 hours of driving will almost top it off the next day. BTW, you should test this out before the trip because the cigarette lighter socket may have a fuse that can't handle the draw of charging the battery.

"Are you claiming a car battery won't work?" Not quite - there is a fair chance that a good car battery will survive a night and if that's the only option it might be the best. But make sure you have a jump start option nearby. Also, an unused starting battery can be used for a deep cycle, but the number of cycles it survives will be limited - maybe a few dozen cycles, maybe only one.

"Can I use the battery on my RV or boat?" This is the one where I have a lot of experience. The basic load of the pump is about 4-8 Amp-hours a night. This is about the same as running a small computer or TV for a couple of hours. Most RVs have (or should have) at least one and maybe two 100 Amp-hour deep cycle batteries, and large boats (and I assume RVs) have 400 or even 600 AH capacity. In other words, the CPAP (without humidity of course) should be a minor addition to the load. Of course, if its a small (or old) RV or boat you should make no assumptions - check with the owner and make sure they understand. If you need to rig an extension (12V extensions can be cheaply had) make sure its a heavier gauge wire so you don't have a voltage drop in the wire. If you're setting up a boat or RV, wire an outlet near the bunk using fairly heavy wire. Another solution is to simple add a battery (such as a scooter battery) for temporary use.

"I'm going camping in a few weeks. The tent will be 50 yards from the car." Get the scooter battery. If its longer than a few nights, get two - they're easier to lug than the big 100 AH battery. If you'll be using the car on occasion, set up a charging system so you can add some juice on the beer run.

"I'll be Off-grid for 6 weeks! What works?" Well, the most straight forward solution is 1 or 2 (or more) larger deep cycle batteries. At 4 AH a day, it really isn't hard to see a solution for a longer period. At some point you run into the self-discharge of the batteries slowly wearing down. Also it would be a real bummer if your 6 week setup died in four weeks, so a fallback plan is needed. [Perhaps my next post will be on solar power options.] And of course, you can always get a generator.

"I'm going white-water rafting - 24 pounds is too heavy. Is there something lighter that doesn't cost a fortune?" Unfortunately, in the lead-acid battery world there is a pretty direct relationship of weight to power. The next size down is a 20 amp-hour AGM (this is the size often found in jump-starters) that weighs about 12 pounds. The good news is that they can be had for only $35, even less if you buy multiples. 20 AH should be enough to run for several nights and be preferable to the larger 35 AH version for more weight sensitive applications.

"What about Lithium power packs?" Please wait for my next post! Also coming up, Solar Power, and more on Charging and Cabling.

Thank you so much, CapnLoki, for all of this detailed and excellent information on different types of batteries, how they work, how they charge, and more! These posts are invaluable for someone like myself who is looking for a solution for when I don't have electricity, yet doesn't understand the complexities of how to safely set up an appropriate and reasonably-priced system. I certainly appreciate your willingness to educate us I agree that your posts on this subject should be on the front page, too

CapnLoki wrote:"What about Lithium power packs?" Please wait for my next post! Also coming up, Solar Power, and more on Charging and Cabling.

CapnLoki wrote:Enough for now. I'll more info on other topics such as lithium options and solar charging later.

I thought I'd bump this thread by asking if the post on lithium batteries is imminent?

ColinP wrote:I thought I'd bump this thread by asking if the post on lithium batteries is imminent?

Coming, but not quite imminent. First there will be one short post about measuring power, necessary groundwork for understanding the specs on Lithium. Also, as I've said many times, I've never used lithium packs with my CPAP, though, like many of us, I have used them extensively with computers and cell phones, and thus much of my advice will be based in theory and on indirect observation. So don't expect any great recommendations, just food for thought. Also, I wanted to touch on Lithium Iron Phosphate batteries, which is a sounder technology, though not as light. And then there's the hobby packs, which have had a big push from the drone fad. The fun never ends.

Hello, do you have experience with the portable power pack appliances? I found a few of these recharchable models (3 in 1, 4 in 1 for example) on the Harborfreight web site. These have the integral 12V outlet which seems a good off the shelf start for "off the grid" activities. I frequently either camp or go sailing in the summer and loathe the thought of the CPAP as a leash. I am new to the CPAP machine as of January 3rd still in the adjustment. I have the Philips Dreamstation with humidifier and heated hose.

southcoast wrote:Hello, do you have experience with the portable power pack appliances? I found a few of these recharchable models (3 in 1, 4 in 1 for example) on the Harborfreight web site. These have the integral 12V outlet which seems a good off the shelf start for "off the grid" activities. I frequently either camp or go sailing in the summer and loathe the thought of the CPAP as a leash. I am new to the CPAP machine as of January 3rd still in the adjustment. I have the Philips Dreamstation with humidifier and heated hose.

Refer to my comments about "Jump Starters" in the third post.

The Harbor Freight units look reasonable, and are cheap, but the "3 in 1" has only a 17 Amp-Hour battery. You could buy this battery for about $30 and a high quality charger for about $25 (BatteryTender) and have a more reliable system. But if you want to use a humidifier, or run more than one night you might think of the larger scooter style "U1" battery that's 35 Amp-hours and a luggable 24 pounds. All the spiffy features of the HarborFreight (or other jump start/power packs) are very cheaply made and are just more things to break. A quality charger will last a lifetime and you can use it with several different size batteries.

BTW, I spend about 3 months every summer on a boat with the Cpap.

Have looked at the solar packs, like the Goal Zero's?

Coloneldad wrote:Have looked at the solar packs, like the Goal Zero's?

As I've said, I have limited personal experience with lithium packs. They work extremely well with cell phones and computers because these devices are designed assuming lithium sized cells. Most cpaps assume 12 or 24 volts, and this is a mismatch that, along with other lithium issues, requires expensive electronics to overcome. And the results are not always successful - refer to Samsung or hoverboards, etc.

Some companies solve this (hopefully) with expensive circuitry, others go cheap with limited support but sometimes they work. They are all based on the same lithium cells, and are surrounded by at least enough circuitry to prevent over/under charging, keep the cells "balanced," and proved several different voltages. This is a quick review I wrote of the Goal Zero a few weeks ago, based entirely on the spec sheet:

"The Sherpa 100 is (seemingly) good quality but is quite overpriced at $300 for 8 Amp-hours. This capacity is the lithium limit for airline travel so you will find a number of packs of this size, starting at about $100. They provide about one to two night's power, without humidity. If weight is not an issue, an 8 AH AGM (sealed lead-acid) battery that weighs about 5 pounds can be had for about $15, and affordable solutions with larger batteries including cables and charger shouldn't cost more than $200."

How Power is Measured
For those wondering why different types of batteries have different types of rating, here's a few tidbits. Care must be taken when comparing ratings for lead acid, lithium ion, and lithium phosphate batteries.

As you've probably noticed, I usually describe battery power in terms of "Amp-Hours" or AH. Formally, this is actually a measure of charge, but as we'll see it's common to use this for power. Since traditionally most batteries used for backup purposes are 12 Volt deep cycle batteries, and these are generally specified in terms of Amp-hours, it works out. To get the total energy, one must multiply by the Volts to get Watts-hours, so a 100 AH deep cycle 12V battery has 1200 Watt-hours of energy.

Watts-hours are roughly equivalent regardless of voltage, or whether its AC or DC, so this is the best unit to use when comparing different types of power. So, for example, a big deep cycle battery has about the same energy of 1.2 KiloWatt-hours, or 10 to 20 cents worth of juice from the wall socket!

One should remember that all of these measures are very approximate, so you have to be careful when stringing them together or you could get meaningless numbers. For instance, 12 volt batteries have a nominal voltage of 12.6 Volts when charged, but this can go go below 12 in normal use. This will affect the Watts it can deliver. Further, the charge voltage can vary from 13.6 to 14.6, so although its useful to simple use "12" it can easily lead to errors of 10 to 20%, Also, charging is only about 90% efficient (Charge Efficiency Factor), so Watts In is definitely not the same as Watts Out. To further complicate matters, the efficiency will vary with temperate, and how fast you're charging or discharging.

The upshot of all of this is that any calculation may be off by 20% or more. Since battery wear is much worse when you discharge below 20-30%, to be conservative its good to think of lead-acid batteries as only having half of their rated power. However, if you've tested a configuration and you've determined it can deliver 80% of its rated power, you can go with that, understand that battery life will be reduced.

Lithium Battery Ratings
Lead acid batteries are built with a number of cells, with each cell actually producing 2.1 Volts. Six cells in series produce the normal 12.6 Volt battery. Lithium cells, have a very different chemistry. The Lithium Ion cells in computers and most battery packs, have a nominal voltage of 3.7 volts. The charge is listed not at the output voltage of the pack (often 18.5 volts when powering a computer) but at the sum of all of the cells at 3.7 volts. This leads to large numbers like "27000 milli-amp-hours" or '32000 milli-amp-hours". However this can't be compared directly to the lead-acid amp hours. What you must do is convert to Watt-hours, by multiplying by 3.7, thus making the 27000 milli-amp-hours equal to 99.9 Watt Hours, which is about the same as 8 Amp-hours from a 12 volt battery.

Lithium Iron Phosphate Battery Ratings
Another type of Lithium battery is the Lithium Iron Phosphate Battery or LiFePO4 battery. This chemistry has a nominal voltage 3.2 V per cell, allowing for 4 cells to make a 12.8 volt battery. Although a bit heavier than Lithium Ion, LiFePO4 batteries have almost identical properties to a Lead Acid battery, making this an ideal drop-in replacement for starting batteries in motorcycles and jetskis. However, there's an odd catch: because Lithium performs much better than lead-acid when depleted (that is, a lead battery at 50% charge might not start a cat, but a lithium battery might) the lithium industry invented a bogus rating called "Lead-Equivalent" or "Pb-Eq" where they essentially triple the actual rating. In other words, they might say "20 Amp-Hours Pb-Eq" when the battery only really has 7 AH when used as a deep cycle. Since batteries with this rating are designed as starting batteries, its probably best to avoid them.

My Backup Battery Setup
Components of my current home setup copied from a recent post, with a few edits:
UPDATED 5/17/2018

Battery: $65
In the original post I listed the MotoBatt, but the price has gone up. Try:
http://www.amazon.com/dp/B00IIZ0IS8 or look for "U1 AGM Battery"

AGM batteries are leak proof and safe for the bedroom - think of all the folks using scooters in the retirement homes. It big enough to run with humidity for a night, or up to a week with no humidity. Maybe three nights if you turn off the heated hose and turn down humidity. There are a wide variety of smaller and larger batteries, but the U1 size seems to be a "sweet spot" for our needs and is relatively cheap and not too heavy to lug around. Should be available at local scooter shops, but shop around for a good price. I saw this in West Marine for $149 - more than double Amazon!

And there is nothing magic about this size battery, you could go bigger with https://www.amazon.com/Universal-UB1210 ... B00S1RT58C (100 AH, $170)
or smaller https://www.amazon.com/Universal-Power- ... B001G8FY38 (20 AH, $38)
or even smaller with https://www.amazon.com/ExpertPower-EXP1 ... B003S1RQ2S (7 AH, $17)

In general weight = power. Mostly true that dollars = power, but caveat emptor!

There's no reason you can't have more than one battery to handle a special situation. You might have one large and one small. Or you might have two or three medium size batteries. If you get extra cables, its easy to switch the charger from one to the other.

Charger: $50
http://www.amazon.com/gp/product/B00068XCQU
This is the medium power tender - if you only need short term (i.e. occasional partial nights) the Junior version will do, and there is a "big" for fast charging or larger batteries. 10 year guarantee, can run 24/7, will not overcharge. I've seen this for less at Costco, and I've seen the bigger 5 amp version for not much more on sale.

Here's the link for the new 5 Amp version. If you have a 100 amp-hour battery, this will still take a few days to fully charge.
https://www.amazon.com/Battery-Tender-0 ... B00EDFPN1O

These "trickle chargers" are designed for gentle, long term use. To put a quick charge on a battery, you can get a larger, automotive style charger. I keep a Shumacker charger in the garage for this purpose. However, the two primary dangers of charging are overcharging (with big fast chargers), and using exposed "alligator" clips. So leave the beast in the garage, and use a small trickle charger in the bedroom.

Here's the link to the manufacturer's site so you can see what's included:
http://www.batterytender.com
The current site does not have nice pictures of what's included in each product. The output of the charger has a "quick-connector." Two additional cables are included, one with "alligator clips" which are NOT recommended, the other has ring connectors that should be attached to the battery.


Cables:
The Battery Tender comes with almost everything including fuses (get spares), but you'll need a "cigarette lighter socket" (or maybe two)
http://www.amazon.com/gp/product/B0041CDPQO $9
If you want to charge while using (UPS mode) and/or add on a cell phone charger or second socket, you want a splitter:
http://www.amazon.com/gp/product/B003L643KS $5

Case: $15
Prevent accidental shorts (if the terminals are shorted it will pass several hundred Amps!):
http://www.amazon.com/gp/product/B006RKCO3I
For larger batteries you'll need a bigger box, but there are plenty in the $10-15 range,

Total cost is under $150 for a 35 Amp-Hour system. The only assembly is bolting the color coded ring connectors to the battery (bolts are often included). The quick connectors are "idiot proof" once you figure it out. I normally don't run off the battery, but if a storm is threatening I can simply plug in my 12V cord. I can leave it charging (UPS mode), or unplug the charger to be isolated from surges.

If you have Respironics get the 12V cord ($25); if its Resmed get the 12/24 converter ($85). Make sure that the cords are matched to your pump; they have the nasty habit of changing the connectors. Use an inverter only as a last resort, since they are only about 60% efficient.

In keeping with my effort to consolidate my battery posts, I'm adding the usage post from Nov 2014, with some edits:

Recently I ran into a nifty little Amp-Hour meter that will allow for reading the power used by a xPAP for a full night. It is marketed for the model RC car and plane market but is useful for measuring any small loads.
http://www.amazon.com/Watts-Meter-Analy ... 001B6N2WK/
EDIT: The original link is broken ... this looks similar:
https://www.amazon.com/dp/B01N5RC6R5?psc=1

This prompted me to sort out my battery backup system and get a new battery. I selected a U1 sized AGM battery - U1 batteries are commonly used for mobility carts and wheelchairs; they weigh about 24 pounds and provide 35 Amp-hours of charge, at a cost of about $65. It is about half the size of a small automotive battery. AGM batteries are lead-acid, but the acid is contained in a fiberglass mat and cannot spill or leak and are often used inside a house.

For a charger I use a "Battery Tender Plus" which provides 1.25 Amp. It is designed for low power trickle charging to maintain batteries when not in use. There is a smaller version, the Junior which is .75 Amp, and a larger 5 Amp version which would be better if you wanted to charge quickly. They all come with a quick connect cable to connect the battery to the charger, and you probably want to add a cigarette lighter socket for connecting to an XPAP. The connections ensure proper polarity. The total cost for the essentials is about $110, with and extra $20-40 for some nice stuff like a box, and additional cables so it can also charge cell phones and tablets, etc. I put quick connectors on the amp-hour meter so I could add it to any circuit and analyze the load. I use the charger full time to ensure the battery is not drained too much at night and can fully recharge during the day.

I've used this for the last few nights to measure the load of my Philips Respironics System One Auto 560. It is set to a pressure of 9 and only occasionally goes up to 10 - the average is 9.2. Ramp is off, and all settings are on the "middle" values. The leak rate is low. Water was topped off and room temp. The first night room humidity was 38% - a bit too dry to go without the humidifier, but I took one for science! Amp-hour numbers are normalized to 8 hour nights.

Results so far:
Night 1 - humidifier off (passive only) 4.07 Amp-Hours 38% humidity
Night 2 - humidifier on 3, plus heated hose 19.34 Amp-hours 38% humidity
Night 3 - humidifier on C3, NO heated hose 19.95 Amp-hours 47% humidity; Classic humidity
Night 4 - humidifier on 3, plus heated hose 19.04 Amp-hours 44% humidity
Night 5 - humidifier on 3, plus heated hose 19.80 Amp-hours 38% humidity
Night 6 - humidifier on 2, plus heated hose 17.12 Amp-hours 42% humidity
Night 7 - humidifier on 3, NO heated hose 11.35 Amp-hours 42% humidity
Night 8 - humidifier on 3, NO heated hose 12.49 Amp-hours 41% humidity
Night 9 - humidifier on C3, NO heated hose 22.88 Amp-hours 42% humidity; Classic humidity
Night 10 - humidifier on 2, NO heated hose 8.96 Amp-hours 39% humidity
Night 11 - humidifier on 2, NO heated hose 7.38 Amp-hours 36% humidity
Night 12 - humidifier on 3, NO heated hose 20.1 Amp-hours 38% humidity Using Inverter
EDIT: Finally got to measure my new DreamStation on boat with NO Humidifier
Night 13 - NO humidifier, No Heated hose 3.82 Amp-Hours; DreamStation Auto
Night 14 - NO humidifier, No Heated hose 3.93 Amp-Hours; DreamStation Auto
Night 15 - NO humidifier, No Heated hose 3.78 Amp-Hours; DreamStation Auto, new meter
Night 16 - NO humidifier, No Heated hose 3.84 Amp-Hours; DreamStation Auto, new meter


A few observations:
As you can see, I bounced around some with the settings as I understood more and wanted to try new things and verify results. There is considerable variation and would probably take a month or so of reading to really get a full picture, but we can start to make rough estimates: The load of the Pump itself seems to be 4 Ah. S1 humidity seems to add about 8 Ah at "3," maybe 6 Ah at "2." The Heated Hose appears to add about 7 Ah. Classic humidity at "C3" without a hose adds about 16-18 Ah, clearly the highest.

A full tank of water is 325 ml or 0.71 pounds, so bringing it from room temperature (say 67 degrees) to the heating plate temp (167 degrees) uses 71 BTU or about 21 Watt-hours or 1.75 Amp-hours. If you can preheat the water, and only fill the amount to be used, you can save a lot of power.

As the water evaporates, it takes heat from the tank; for the entire tank this comes to about 18 Amp-hours of battery power. In Classic Mode, I think the plate maintains a constant temperature, but the power used will vary according to how much water actually evaporates. which will depend on many factors. In S1 mode, it tries to maintain a a constant humidity, but again, it depends on many factors. And of course the heated hose doesn't add humidity, it simply prevents "transmission loses" in the hose, but at a considerable cost.

The water usage was roughly half a tank per night - in line with the power draw. I would expect much lower water usage (and thus current draw) in the summer with higher ambient humidity. I could not closely correlate water usage with current draw.

Unfortunately I can't quantify the comfort level - I tend to vary between "no so bad" and "why am I so parched?" randomly and its hard to remember in the morning how bad it was. Clearly the "no active humidity" was the worst, but I've lived with that many times while travelling or on my boat so I guess it doesn't bother me that much, as long as the ambient humidity is not too low. With power to spare, especially in the dry season, I'll use the humidifier, but its nice to know I can get by without it.

Night 12 was really a test of inverter efficiency under "real world" conditions. Comparing to the two similar runs using direct DC, this implies lower than 60% efficiency - in line with the ResMed battery doc and my tests from 2013. The inverter is a cheap Bestek 150 Watt from Amazon.

Nights 13 and 14 were using my new DreamStation Auto with no humidifier or heated hose attached. The settings were the same as my older 560. The result from the new "bare pump" is essentially the same as for the old machine. Nights 15 & 16 are using a new meter.

Here's a link to the ResMed battery guide. It shows the ResMed S9 AutoSet using perhaps a tad more power than the Respironics 560. There's no way to directly compare humidifier draw, but the results are similar.
http://www.resmed.com/us/dam/documents/ ... lo_eng.pdf
Although the basic AirStart 10 has a similar draw to the S9, the AirSense 10 uses 0.93 amps or 7.44 amp-hours for an 8 hour night. This is almost double the load of the comparable Respironics machine. If you goal is low power use for a new bare pump, the Respironics is a much better choice.

There have been a number of posts here that confirm these results. Also, remember that low pressure, such as 6, will use significantly less power; high pressure more. Also high altitude use more power.

What about the use of a lithium ion battery?

What about the use of a lithium ion battery?

Go back and read from the beginning of the thread.