CPAP battery for backpacking
June 3, 2022 2:23 PM   Subscribe

Need to figure out how many hours I'll get on each battery based on my machine/pressure.

Trying to buy a portable battery for my travel CPAP machine. I'm considering some options but don't know enough about electricity to figure out how many hours I'll get out of each one (I cant trust the marketing materials since it'll vary by the machine/pressure, etc), and many of them say they will last 50% longer with travel CPAPs. Price is less important than use time/weight. Ideally I'd like it to weigh as little as possible, but also need it to last for at least 2 full nights of sleep (7-8 hours).

1) Do you need to use a CPAP-specific battery? Or could I use any portable battery?

2) Can anyone tell me how long each battery will last? Info below for mine and each option.

MY CPAP:
Breas brand Z2 Auto, pressure setting is 7
30W Power Adapter
Unit Input range 100–240V, 50–60Hz
Typical power consumption 20W (30VA)
Maximum power consumption 35W (70VA)


OPTION 1:
EXP48PRO
Needs a DC power cord
Weight 3.25lbs
Capacity: 153.6-Watt Hours (Wh)/12.8 Amp Hours (Ah) @12V / 48,000 MilliAmp Hours (mAh) @ 3.2V.
Main DC Round Output Power Port: 12V@10A Continuous/15A Peak (5Min)
Type C Input DC: 5V@3A / 9V@3A / 15V@3A / 20V@2.25A.
Type C Output DC: 5V@3A/9V@3A/12V@3A/ 15V@3A /20.3V@3A
Lifecycles: Up to 5,000


OPTION 2:
Portable Outlet UPS Battery
Weight: 2lbs, 14ozs.
Battery Capacity: 159 Wh/14.4Ah
AC Input: 100-240V/50-60Hz
DC Input: 12-19V, 2-3.2A
AC Output: 110V/60Hz
USB DC Output: 5V, 3.0A
Rated/Peak Power Output: 100W/145W


OPTION 3:
Zopec VOYAGE Universal SMART CPAP Battery
Capacity: 150 Wh (40,000 mAh)
AC Output 110V/60Hz/100W
about 2 lb


OPTION 4:
Z1 and Z2 PowerShell with Extended Life Battery
Specifically made for my travel cpap
lightest one at 1.58lbs (with the little case that holds them together)
Battery Type 14.4v Lithium Ion Battery Pack
Battery Capacity 99.4 Watt Hours
Battery Size PowerShell = 6.00 x 4.25 x 3.00 Inches
Extended Life Battery = 6.125 x 4.00 x 1.375 Inches (Approx)
posted by Autumn Willow to Technology (9 answers total) 4 users marked this as a favorite
 
I haven't looked at your specifics but you do not want to plug your ac adapter from your cpap into anything. you'll be converting DC power to AC and then back to DC, generating a ton of heat and killing your battery 2-3x as fast.

you want to buy DC adapter for your cpap that plugs into your battery pack. when I looked it was like $75-100 for my cpap for just the power adapter. it ends in a 12v cigarette lighter (they may have modernized this) that you plug into your battery pack.
posted by noloveforned at 2:52 PM on June 3, 2022 [1 favorite]


so yeah, I'd say options 1 or 4. the heavier one will likely last about 50% longer based on the watt-hours.
posted by noloveforned at 3:05 PM on June 3, 2022


Response by poster: Thanks! And yes, the 1st option comes with a DC power dord so it can connect directly the machine and the power bank. The others just have an AC port so I can plug my regular AC cord for my CPAP right into the power bank.

If anyone can calculate/estimate how many hours each machine would last that'd be great!
posted by Autumn Willow at 3:17 PM on June 3, 2022


By dividing Watt hour ratings by the Watts you need, you get the hours it will last. This calculation will probably be optimistic, and you'll do a little worse, because nothing is 100%. What nolove says is especially true: the AC output devices will be somewhat less efficient than the DC output devices.

So by that simple calculation alone, the first one and maybe the last one might last most of one full night, when brand new, and probably the others won't. None of these options will last anywhere near two full nights, unfortunately.
posted by fritley at 4:20 PM on June 3, 2022


1) You don't have to use a cpap-specific battery, but it should be a deep-cycle type. We use Marine deep-cycle batteries for our CPAPs when camping. We each had one, but turns out mine didn't accept a charge after spending all winter on the trickle charger, so was DOA on Memorial Day.

We ended up both using a single battery, and an inverter (because the DC adapter for her brand of machine is hella expensive). We got exactly three nights out of it, as it started beeping about low battery about the time we woke up on the third day. But it's way too heavy for hiking around with.

2) What you're really wanting to look at is the AmpHours of the battery and compare that to the current draw (in amps) of your machine. I calculated ours using a max 2A draw (which I think is conservative in our case) from each machine. So, 2A x 2 machines x 3 nights x 8 hours = 96Ah total usage, which is right about what the battery is rated for.

Based on your desire for 2 nights for just your machine, you'd be wanting a capacity of 2Ax2nightsx8h = 32Ah capacity.

Back of the napkin math suggests #1 or #3 would suffice. #2 would not last 2 nights, and #4 is dicey if I'm doing the math right (since it doesn't supply Ah capacity I had to convert from the W(att)h figure).

This link is specific to ResMed, but it it has a table in it that you can use to figure out what Ah capacity you need based on your machine's consumption. I looked at your specs but cant quite work out how to convert the numbers it provides into current draw that is used by this table, but it could be useful.

I'd be interested to hear what you end up using and how well it works for you!
posted by SquidLips at 4:22 PM on June 3, 2022 [3 favorites]


Response by poster: @SquidLips, thanks for the info! If we get 32Ah capacity for my machine, I'm not sure how you found #1 or #3 would suffice, since those say 12-14 Ah. Basically, where do you go from 32Ah to figure out how long the battery will power it?
posted by Autumn Willow at 4:39 PM on June 3, 2022


So for #3 it lists 40,000mAh, which would be 40Ah. I just now realized that your specs for #1 list different Ah capacities depending on the voltage, which first of all I didn't see at first, but secondly it kinda threw me as I wasn't aware that Amp Hour capacity depended on the voltage - I mean yeah, Amps is a function of volts and watts, but it should have a consistent capacity I would think, but I'm not knowledgeable enough about this stuff to be sure. I just assumed that something that said it had a draw of, say, 2Ah would last 5 hours on a 10Ah capacity battery; e.g. it's the voltage / wattage of the draw (your cpap) that determines the Amp Hours it consumes. Very possible I'm missing something in the equation so apologies if that's the case.
posted by SquidLips at 4:51 PM on June 3, 2022


You don't want to use anything that converts battery DC to AC and then back to DC for the machine. That's going to waste a lot of energy in the conversion, so you'd have to carry a heavier battery and the electronics to handle those conversions. That disqualifies your options 2 and 3.

So you can either use option 1 or 4 or put together some kind of brew your own solution that might be a little cheaper using a non-CPAP specific battery (it doesn't matter, a battery is a battery in this context as the power draw is low and constant). But if you're not comfortable with wiring and such, you probably don't want a DIY solution.

Your option 4 says it lasts 1-2 nights, so you'd probably need two of them, though it wouldn't hurt to buy one, try it out at home and buy another if you need it. Your option 1 is 154Wh, which is roughly 1.5 as much energy as the 99.4Wh of your option 4, so you can expect 1.5-3 nights from it. Again, I'd buy one and try it out at home.

Certainly option 1 is a better deal at 1.5 times the capacity, though it might be a little more annoying to have a cable in the mix instead of something that just plugs right into your machine. On the other hand, option 1 will let you charge your phone or anything else that charges via USB, while option 4 will not, so if that's valuable to you, definitely get option 1.

It's not clear to me why Breas says your machine typically consumes 20Wh, but then says a ~100Wh battery will last 1-2 nights (100Wh/20Wh = 5 hours). I'd assume they are saying you need to change your settings to ones that use less power in order to have the battery last that long. You might want to search some of the CPAP forums to get real world reports on how long the Breas battery really lasts in typical use.

Just as a general note, it is much easier to look at these calculations using watt hours (Wh) which are a measure of the amount of energy, rather than amp hours (Ah), which are a measure of electrical current and have to multiplied by voltage to get watt hours. Watt hours don't change depending on battery voltage, amp hours do.
posted by ssg at 5:32 PM on June 3, 2022 [1 favorite]


I looked at this for ResMed devices and decided I'd buy the official ResMed battery. It's about twice as expensive (retail) but having it fully integrated and designed for the purpose seemed worth it. One nice thing about the Breas PowerShell, the official option, is that it seems to clip directly on to the CPAP making one small compact unit and no extra wires.

Mentioning this for future seekers: if your CPAP has a humidifier or heated air option that draws a lot more power than just the CPAP pump. Consider turning that feature off when you need battery. (The Breas unit doesn't seem to have heating or a humidifier.)
posted by Nelson at 7:23 AM on June 5, 2022


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