Choosing a Battery

[Krelvin]

Good stuff here.

[LoBattery]

I like those little GT POWER meters and use several of them around the solar powered camp. Before I got an autoset machine, I used to look at peak wattage in order to get an idea of how bad the leakage was that night. They will also tell you how low the voltage dropped that night giving insight to potential bad battery connections. I wouldn't use a FLA battery without one to monitor how much power was taken out of the battery. There are about four variations available. A metal case version can be had for less than $10 which has no screen illumination. Keep a flashlight handy to read it.

[deeve]

Hello and thank you very much for this information @CapnLoki I am going to get a U1 35AH AGM battery setup like you outlined for Jeep camping with my son. You mentioned charging the deep cycle from the car cigarette lighter. I am having trouble finding something, or understanding if what I am thinking will work and was hoping you could advise.
I will have one of these coming out of the battery box
https://www.amazon.com/Battery-Tender-0 ... ery+tender

If I take one of these and plug it into the Jeeps cigarette lighter for, say an hour, will that give me a boost in juice without killing the battery prematurly?
https://www.amazon.com/Deltran-Battery- ... er+adapter

Any recomendations for monitoring the current state of the battery for charge levels/power left?
Thanks!
DAVE

[CapnLoki]

...
If I take one of these and plug it into the Jeeps cigarette lighter for, say an hour, will that give me a boost in juice without killing the battery prematurly?
https://www.amazon.com/Deltran-Battery- ... er+adapter

Any recomendations for monitoring the current state of the battery for charge levels/power left?
Thanks!
DAVE

No, actually I don't think this works! Unfortunately I don't have one of those plugs, but here's the problem: this plug is intended to charge the car battery from a BatteryTender charger. The BT charger plug is Positive on the male (bare) side so the cord with the cigarette plug is Positive on the female (socket) side. The battery cable is also intended to connect to the charger so it has the same configuration as the cigarette plug. Connecting them together essentially shorts the car battery to the deep cycle positive to negative, which is a meltdown situation.

The solution is to reverse the wires, being very careful to label things, because its an inherently unstable situation. If you use the car a lot for camping, you might permanently connect a plug to the car battery. Another solution is to use the 1-to-5 splitter, and then connecting both to the "5" side of the splitter, since this is effectively male-to-male and female-to-female connections. Or you can use the alligator clips. Whichever method you use, I strongly advise using a digital voltmeter which shows the positive/negative voltage to check things out. Remember whatever you're doing, the positive always connects to the positive.

I knew that eventually someone would ask this question - I've been dreading it!

Another problem is that the cigarette socket is sometimes fused and often turned off when the car isn't running. This shouldn't be a problem with the 35 AH battery since it shouldn't charge over 10 amps, but a larger battery might cause a problem.

As for "state of charge" meters, this is a major disappointment. There's no easy way to do this. All sorts of devices claim to measure charge level but basically they check the voltage and guess. With practice you can get a rough idea, and if it measures under 11.6 you can be pretty sure its near empty. But if it reads 12.1, it can be anywhere from 30% to 70%, so you really have to use some extra knowledge. In my usage post I mention an Amp-hour meter used by the model car folks that's the only thing I've seen for under $200 that works. But these meters have to be wired inline, and I haven't seen a small one that works for both charge and discharge cycles. On boats/RVs these meters cost about $300 and they still have issues.

[Guest]

It is best to measure the battery voltage when it is under a load, meaning the cpap is powered on, then it should not be under about 10.5 volts. Much less and it may not even turn on or stay turned on. When a cpap cycles on then off repeatedly it is normally a sign of under voltage or under current which can be the battery OR the wiring is not large enough to carry the amps needed to keep the cpap powered ON, or simply a poor (bad) connection in the wiring causing a voltage drop across the bad connection and delivering less to the cpap.

So no matter what you use to check the battery do it with the cpap powered ON.

[deeve]

Ahhh. Thanks. I get it now. I wasn't thinking about the pos neg but your right. Ill work around that. Thank you.

[deeve]

Quick followup question..I found a male to male adapter that should run between the car cigarette style power port to the battery. Since the vehicle is regulated at 12 volt, I will not need any other kind of regulator since the deep cycle battery will not (Should not) pull more than 10 amps, correct? Eventually, I will put a dedicated SAE plug from the battery after I get my vehicle aux power center squared away.

[CapnLoki]

Quick followup question..I found a male to male adapter that should run between the car cigarette style power port to the battery. Since the vehicle is regulated at 12 volt, I will not need any other kind of regulator since the deep cycle battery will not (Should not) pull more than 10 amps, correct? Eventually, I will put a dedicated SAE plug from the battery after I get my vehicle aux power center squared away.

The car regulator should be fixed at about 14.2 to 14.4, and you should be able to measure that with a digital voltmeter. Fancy chargers go through various stages to maximize the charge rate, and then taper off to a trickle, but you won't find that on a car alternator. It probably doesn't "turn on" at low idle, so unless you're going somewhere, you'll want to rev it up a bit. You'll need a voltmeter to determine the optimum point, but it should be between 1400 and 2200 RPM.

Batteries have an "Acceptance Rate" which tells how much of a charge they will accept, at a given voltage and discharge level. The rule of thumb for this type of battery is about 25% of the amp-hour capacity, or about 9 Amps for a 35 AH battery. This assumes fairly deep discharge and a high charge voltage, so you may never see this level. Although a 50% charged battery can accept a fair current, that tapers off so that the last 10% can take a long time. This leads to protocols for boaters and RVers like: "Battery capacity should be triple a day's usage" and "Discharge to 50% and then charge to 85% with about an hour and a half engine time." If you don't use humidity and your usage is around 5 AH, you probably want to run for 2 or 3 nights, than go on a hour drive for beer. This is a very conservative protocol; you could push that a fair amount.

As for fuses, I would guess the car has a 10 to 15 amp fuse on the socket. Definitely carry spares including a variety of sizes. The BatteryTender cable also has a fuse, and probably your CPAP cable. Carry spares for everything!

[ShockShag]

Hopeful that this is a good place to ask this rather than start another post. Is there an easy way to find the ah requirements of various machines? I have been looking at a Devilbiss Intellipap since it has a DC cord and is closer to cheap than other dc capable machines, but I cannot find the ah requirements. The machine I use at home as backup, with a massive deep cycle marine battery, is an ancient machine and uses 3ah/hr so taking it camping/kayaking is not possible. Reading this thread it appears newer DC capable machines use dramatically less ah's.

[Goofproof]

Hopeful that this is a good place to ask this rather than start another post. Is there an easy way to find the ah requirements of various machines? I have been looking at a Devilbiss Intellipap since it has a DC cord and is closer to cheap than other dc capable machines, but I cannot find the ah requirements. The machine I use at home as backup, with a massive deep cycle marine battery, is an ancient machine and uses 3ah/hr so taking it camping/kayaking is not possible. Reading this thread it appears newer DC capable machines use dramatically less ah's.

Under 3 AH on D/C not 3ah/hours is about avg for normal XPAPs, however different models and types and settings (pressures and exhale relief) will vary current draw. This is not taking into account.Converting D/C to A/C/and back to D/C, or running a HH. Running transmitters that send you data also consume power in new unit, even leaving them plugged in while off uses electric in some. Jim

[CapnLoki]

Hopeful that this is a good place to ask this rather than start another post. Is there an easy way to find the ah requirements of various machines? I have been looking at a Devilbiss Intellipap since it has a DC cord and is closer to cheap than other dc capable machines, but I cannot find the ah requirements. The machine I use at home as backup, with a massive deep cycle marine battery, is an ancient machine and uses 3ah/hr so taking it camping/kayaking is not possible. Reading this thread it appears newer DC capable machines use dramatically less ah's.

The best guide for Respironics is my usage guide. For ResMed, there is a battery guide; this is (I hope) a current link:
http://www.resmed.com/us/dam/documents/ ... lo_eng.pdf

Other current brands should be comparable, but there is no easy way to tell. The specs generally list the maximum power or current of the power supply, which bears no direct relationship to the actual usage averaged over a night. It should be possible to find a Respironics 560 for under $500, less in the gently used world. A pump only 560 might be only $300.

[jpek]

CapnLoki, thank you for the info, but I have to admit that as a rank beginner I feel pretty overwhelmed and confused. I know very little about batteries, electrical issues inverters (don't actually know what they are), or all the associated abbreaviations. I'm not sure how to estimate my needs, what kind of battery to buy, how to charge it or how often. Where does a total beginner start?

I have an APAP, which usually stays at 13 pressure. I do use a humidifier, currently set to 2, heated hose but currently not heating (set to 0). I'm looking for a cost efficient and somewhat portable battery solution to use for camping (a couple of nights at a time, with car nearby) and the odd power outage at home.

[CapnLoki]

CapnLoki, thank you for the info, but I have to admit that as a rank beginner I feel pretty overwhelmed and confused. I know very little about batteries, electrical issues inverters (don't actually know what they are), or all the associated abbreaviations. I'm not sure how to estimate my needs, what kind of battery to buy, how to charge it or how often. Where does a total beginner start?

I have an APAP, which usually stays at 13 pressure. I do use a humidifier, currently set to 2, heated hose but currently not heating (set to 0). I'm looking for a cost efficient and somewhat portable battery solution to use for camping (a couple of nights at a time, with car nearby) and the odd power outage at home.

First inverters: they convert battery power to AC power so that regular appliances can be run from a 12v battery or a "cigarrette lighter" outlet in a car. They claim 90% efficiency but actually are 60% so you should avoid them if possible. Your apap can run from a battery directly with cable that cost $25.

Your machine is similar to mine, so you can use the usage post above to guess your needs. Your pressure is higher than mine, so you might add an amp-hour to the needs.

The battery I recommend for many is U1 size AGM - its 35 Amp-hours, which will power your apap without humidity for maybe 4-5 nights, or with humidity and heated hose for 1-2 nights. Its a luggable 24 pounds, cost $65. AGM are safe to move around, they can run upside down. I use a BatteryTender charger, which comes with most of the cables needed; assembly is bolt on two color coded connectors. All is explained in a post above.

[Princess Tia]

Forgive me, another electricity "dummy" here...

You've posted a lot of good information here, but I can't parse it all. And I'm not sure how it applies to my situation, which is this: I'm going to be car camping for about a week, with no access to "the grid." I want to be able to use my CPAP every night (pressure is 13 mm, no humidifier). I will NOT be driving the car around while there, and when the car is turned off, there is no power to the cigarette lighter, so cannot use that to recharge a battery.

I had originally thought to use a li-ion battery such as this one and charge it during the day with a portable solar charger. But another constraint on this project is an extremely tight budget, and this simply costs too much.

I was heartened to see your more cost-effective solutions. Now I'm looking at this 45ah battery and hoping I won't need to recharge it at all during the trip. Does that sound feasible to you?

I had some questions about the other things you talk about in your posts.

Battery tender: If I understand correctly, this is a device to recharge the 12V battery and maintain its charge during storage. I assume that it plugs into a wall socket and is connected to the battery terminals.

The Battery Tender comes with almost everything including fuses (get spares), but you'll need a "cigarette lighter socket" (or maybe two)

Is this cable used to help recharge the battery from the car cigarette lighter while driving? If so, I wouldn't be able to use it. And I understand the concept of the splitter (I do have several USB devices to also charge), but how does it get used? Which end plugs into what? (I warned you I was a dummy! )

TIA

[HoseCrusher]

It all starts with measuring or finding how much energy your machine uses. A reasonable estimate is somewhere in the 4 - 8 amp hours a night. Let's pick a number... how about 6.

If your machine uses 6 Ah a night and you have a 45 Ah battery and the battery is actually capable of delivering all its capacity...

45/6 = 7.5 nights of use.

So far we have a good theory but don't really know how things will work out. You can do a test to see if these assumptions are close and then you will know for sure. An alternative is to purchase 2 batteries.

The Battery Tender is used to charge the battery back up. I believe it can either be used from household current or from your vehicle charging system. That means the engine needs to be running in order for it to work, or you need to plug it in to household current.

The big question is how much does your machine use, followed by what is the actual capacity available from the battery. Many times the battery capacity is optimistic.