Choosing a Battery

[TheBigTenor]

What is your take on these small self-contained battery back-up power generators for use with CPAP's?

I was preparing long list of sarcastic remarks based on the term "power generator" when in fact it generates nothing, but on close inspection it seems to have reasonable value for the money. 155 Watt-hours for $140, DC outlets, AC inverter. Your AirSense will need a 12/24V converter from ResMed, and it will use almost 100 Watt-hours at pressure 10 so this will be good for one night without humidity or heated hose. You might get pushback from the airlines which often have a 100 WH limit. For a one night camping trip this looks fine, especially if you value light weight. Don't assume you can recharge it for the next night by running the car for 20 minutes - it looks like it would be 4-7 hours to put back enough for another night.

Well, since I need my AirSense 10 (I run 6-11 pressure [rarely go above 9]) running 3-4 humidity level for 7 hours, I might want to look elsewhere? I was looking for a one-two night easy to carry source for a weekend camping trip. Looks like I'd get one night with it according to your estimation? Although it might be good for a one night emergency at home. Marine batteries are a bit tough to carry when heading out to camp.

[CapnLoki]

Well, since I need my AirSense 10 (I run 6-11 pressure [rarely go above 9]) running 3-4 humidity level for 7 hours, I might want to look elsewhere? I was looking for a one-two night easy to carry source for a weekend camping trip. Looks like I'd get one night with it according to your estimation? Although it might be good for a one night emergency at home. Marine batteries are a bit tough to carry when heading out to camp.

Going by the ResMed Battery Guide:
https://www.resmed.com/us/dam/documents ... lo_eng.pdf
The AirSense at pressure 8 humidity 4 draws 2 amps from a 12V battery using the 12/24 converter. This means 2x7hours = 14 Amp-hours. Your battery is 155 watt-hours, dividing by 12 means it about 12 amp-hours so this looks like it will run out an hour short! If you use the heated hose it will be much worse.

My experience is that although I crave the humidity at home, especially in the dry winter, when I'm outdoors or travelling to a humid area the humidity is enough that I leave the humidifier at home. On the other hand, camping in Palm Springs may require added humidity. If you can forego the humidifier, and stay at 7 hours averaging pressure 8, you have a fair chance of squeezing 2 nights out of the battery.

As for "marine batteries" you should forget that term - on my boat I have 6 "marine" batteries: two are starting batteries that would die an early death if used in a deep cycle application, the other four are traditional flooded batteries, where the sulfuric acid would eat a hole in your foot if you spilled it! You want an AGM battery, as described on the first page of this thread. The U1 size is a luggable 24 pounds and provides 35 amp-hours. You should get 2 nights with a margin with your setup. For longer periods, you can get a bigger battery (or additional smaller ones) for not that much money, but it would be quite expensive with lithium packs.

[CrazyCooter]

Performing my own experiment tonight in my search for a super compact, safe, overnight moto camping battery option.

So far my Dreamstation Bipap Auto SV Advanced appears to draw an average of .5ah bouncing between 5 and 10cm without heat or humidity on. Will be using the shielded 12v cig lighter adapter.

Purchased an Ah counter for another project so I wired it up to a Yuasa YTZ20-BS AGM cycle battery I had laying around beside to run on tonight. https://www.amazon.com/MICTUNING-6-5-10 ... way&sr=8-2

It's looking like a LiFePo4 9Ah battery will do the job, much more stable/safer than LiPo, can be charged enroute on my motorcycle, and much lighter/compact than AGM batteries. Been eyeballing this one:https://www.bioennopower.com/collection ... -blf-1209w

[hiker]

CC their site says:

CPAP machine, medical equipment or scientific instrumentation. Television sets and speaker sets cannot be used.

But what do I know? . . . about electricity.

[CrazyCooter]

I did not see that, but it's probably just CYA. No reason a clean DC output cant be used for our application. I wouldn't use a lithium battery in this application for sure.

I ran it 2 nights and will be using it on the road this weekend.

[hiker]

Using an inverter?

I was wondering what I could use and stumbled on this:

https://www.subaruforester.org/threads/ ... sco.65840/

' . . .And especially with inverters, do the math. They're usually specified in Watts of output. Double that for starters to account for inefficiency in the inverting process and determine Watts of input. Then, since Watts = Volts times Amps, divide by 12 to determine the Amps that the inverter is going to try to take out of your accessory circuit. You might be surprised at how large a number you end up with. And it's Amps that create the heat when flowing through resistance, and heat goes up in proportion to the square of the Amps.
'

The guy is a super moderator so I assume he knows what he is talking about. My forester has two cigarette sockets, on is 10Amp and the other has a 20 Amp fuse, but if this guy is right the wiring is probably worse than the fuse?
Doing his math in reverse, than the 20 Amp should not use an inverter over 120 Watts.

[CapnLoki]

Using an inverter?

I was wondering what I could use and stumbled on this:

https://www.subaruforester.org/threads/ ... sco.65840/

' . . .And especially with inverters, do the math. They're usually specified in Watts of output. Double that for starters to account for inefficiency in the inverting process and determine Watts of input. Then, since Watts = Volts times Amps, divide by 12 to determine the Amps that the inverter is going to try to take out of your accessory circuit. You might be surprised at how large a number you end up with. And it's Amps that create the heat when flowing through resistance, and heat goes up in proportion to the square of the Amps.
'

The guy is a super moderator so I assume he knows what he is talking about. My forester has two cigarette sockets, on is 10Amp and the other has a 20 Amp fuse, but if this guy is right the wiring is probably worse than the fuse?
Doing his math in reverse, than the 20 Amp should not use an inverter over 120 Watts.

I'm not sure what your point is. Inverters are not advised for running a cpap from a battery because of their low efficiency, and running from a car's starting battery is not advised because that's a formula for killing a battery.
Perhaps if you explained what you wanted to do, and what your equipment is, we could help you find a solution.

[hiker]

Thanks

No, I am not thinking of running the CPAP direct off the car battery with the car ON or OFF.

I have several options while off the grid:

I got the setup that you and camper van worked out on page (tab?) 12 of this thread for car camping.
I have the transcend larger battery which gave me over 2 nights at home (sea level) brand new.
I got the Maxoak battery which did. not recharge so I hope to get a replacement in a day or two.
https://www.amazon.com/MAXOAK-Airsense- ... FY5BN85YJ1

Most of the time I foresee recharging this at home or in a motel room, or maybe a campground with electric hook up.

MY CPAP is the Transcend minicpap and the Res Med Air Sense 10 which have worked with the "scooter?" batteries and the ResMed with the MaxOak and the transcend with its P8 battery.

Just looking at transcend mini, it looks like it comes with a "mobile: adapter to charge for a car or solar panel.

I think the MaxOak would need an inverter? It might be a too heavy for backpacks, expect short ones to a base camp.


Not sure about the scooter batteries. Maybe a male to male plug with the right polarity?

This would only work if I have along drive between camps and hikes, and likely only charge one of these batteries.

Another option would be using the scooter batteries to charge one of these smaller batteries?

EDIT

Here is another battery option, good reviews not sure how many years these will last though
https://www.amazon.com/TalentCell-Recha ... 7QXMA&th=1
EDIT3 (I think I found these from this other post:
viewtopic/t172420/Trekking-with-Z1-APAP ... it=battery
)
Can recharge in car with their $8 adapter.
Anyway my comments were in response to various threads, talking about blowing fuses in the car trying to use the car to charge from.

[hiker]

I have something like this but from craftsman:

https://www.amazon.com/gp/product/B004Z ... 3WKDBWEWZ2

I could post a picture if that helps.

This trickle charges a dead car's battery from a good (running) car.

Do you think this would be ok to charge CPAP batteries while I am driving my car, plug the running car end into my car and the other end into the Cap battery that is to be charged?
It has a junction box that allow you to test the charge of the battery being charged to see if it can start a car not sure what else it does.

I don't think these are used much anymore, for one they are slower than jumper cables and they also make battery packs to jump a car, which tow trucks used on my car the last time it needed it.

(I wonder why the other male to male plugs I have seen have a polarity, ie why you don't just reverse the direction of the cables like this does?)

[hiker]

If anyone is interested, I used an old Radio Shack inverter to recharge a Scooter Battery after one night's use. I did not check how the charging was doing until I drove 6 hours. I used the same 3 amp charger I use at home so was thinking at least this would not blow a fuse.

The next day I recharged the MaxOak after about 2 hours, plugging in their charger. The inverter was working very hard (noisy), but did not blow the car's 20Amp fuse.

175 W inverter

12XDC to 115VDC, 11,5-15.5 VDC range

Output
115/AC/175W continuous power peak power 350W

Surprised this worked, the maker? of the MaxOak recommended a 300w inverter but 300/12 = 25 AMP which would blow a fuse, assuming it would draw that much.
(But what do I know)

I did not try using the car to car trickle charger. That should be more efficient (faster?)?

[hiker]

https://batteryguy.com/kb/knowledge-bas ... comment-44

If I understand this article, for the battery shown, drawing the battery down to 50% is as bad as 100%.

While 50% gets twice the cycles, each cycle is half the power ?

70% is much much better.

Using a volt meter on a battery at room temps, that hasn't been used for awhile should be

"The terminal voltage on a battery at 70% state of charge should be around 5% above the stated voltage of the battery. So for a 12 volt labeled battery you should see a voltage of around 12.6V."

My 100% charged battery is about 12.6 maybe because it is a smaller battery, no idea what it is at 70%,

'If the voltage you see is substantially below this, especially if it is below the stated voltage of the battery (in the case above this would be below 12 volts) you are heavily discharging your battery and dramatically decreasing its lifespan.'

Or maybe my voltmeter is not that accurate. I think it has been above 12 volts so far.

[Jack Burton]

My 100% charged battery is about 12.6 maybe because it is a smaller battery, no idea what it is at 70%,

No idea what you have for a battery but 12.6 volts is the max voltage for a 3s?p lithium ion battery pack.
That is 3 cells in series x 4.2 volts.

[CapnLoki]

https://batteryguy.com/kb/knowledge-bas ... comment-44

If I understand this article, for the battery shown, drawing the battery down to 50% is as bad as 100%.

While 50% gets twice the cycles, each cycle is half the power ?

70% is much much better.

I think he overstated that. First of all, each battery is a bit different so you really have to look at each one. Also, taking a lead-acid battery down to zero is always very bad, not just twice as bad as going to 50%. In fact, I've generally seen charts that essentially say going to 20% charge is twice as bad as going to 50%. For example:
https://www.trojanbattery.com/markets/r ... energy-re/
I'm thinking the batteryguy chart is actually a misprint (or just made up). A lot depends on how often you're actually using the battery. When I'm living full time on the boat, I cycle between 85% charged (its tedious to get to a 100%) and 50% discharged, and this gives me about 6-7 years from Trojan flooded batteries (T105's). However, it you're only using the battery a few dozen nights a year you might as well drain it down to 20% because you're probably not ever going to use it more than a few hundred times.

Using a volt meter on a battery at room temps, that hasn't been used for awhile should be

"The terminal voltage on a battery at 70% state of charge should be around 5% above the stated voltage of the battery. So for a 12 volt labeled battery you should see a voltage of around 12.6V."

My 100% charged battery is about 12.6 maybe because it is a smaller battery, no idea what it is at 70%,

'If the voltage you see is substantially below this, especially if it is below the stated voltage of the battery (in the case above this would be below 12 volts) you are heavily discharging your battery and dramatically decreasing its lifespan.'

Or maybe my voltmeter is not that accurate. I think it has been above 12 volts so far.

"5% above the Stated Voltage" is a very odd way of saying it. "12 Volts" is just an expression - everyone knows that the nominal voltage is 12.6 to 12.8 for a fully charged lead-acid battery, and 12V is just a rough reference point. Each battery will be a bit different,and although the official guides give a suggestion, the recent history can affect any reading. Here's the Trojan guide, which indicates 70% would be about 12.5V for their AGM (page 22):
https://www.trojanbattery.com/pdf/Troja ... sGuide.pdf
They are using "open circuit" readings, or no load. A heavy load can easily drop the voltage well below 12V but that doesn't mean the battery is being damaged. When my fridge runs at the same time that the TV is on - about a 10 amp load - the voltage can drop below 12, and the battery is not being damaged. And the microwave or anchor windlass can put on a 100 amp load which certainly drops the voltage.

The size of the battery is not relevant, all lead-acid batteries are using the same chemical reaction, but there are small differences in the manufacturing that change readings by 0.1 or 0.2 volts.

[hiker]

Above where he says the battery will be 5% higher or 12.6 V at 70% charge he says:

'Checking the terminal voltage of a lead acid battery – a fully charged 12 Volt battery can display an actual voltage up to 10% higher.'

Or 13.2 at 100% so for whatever reason I am not getting that.

Thanks for responding, I do think (agree) that he may have made some of this up for the article.

"a year you might as well drain it down to 20% because you're probably not ever going to use it more than a few hundred times."

This is probably a very good point in my case.

======

Jack I have several batteries, but I mean't to refer to the smaller scotter battery that Campervan said he was getting.

[laprof]

Since I'm in the Maritimes for a few months - where power outages are not unusual - I decided to buy a battery for my Resmed Airsense10. I ended up with a Midestrom. It's light weight (under 3 lbs) and easy to use. Well, Dorian hit here on Saturday, so I had to put the battery to use! It worked beautifully. I had it on for about 8 hours (after turning off the heating for the tube and distilled water) b/c I read with my CPAP turned on before sleeping. The next day, I still had 2.5 of the 5 lights left for power, enough power for a 2nd night. A neighbor lent us a generator for 3 hours (phone needed charging, fridge needed a bit of help, and I wanted to charge fully the CPAP battery). I know that it's an expensive battery and it likely won't last for more than 2 nights without charging, but it has been a Godsend for me. Best.