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Battery usage, while camping
(05-12-2017, 08:54 AM)Sleeprider Wrote: Most of the above responses assume that you are using the humidifier.  The actual amperage draw is much lower if you do not use a heated humidifier and hose, and use a direct 12 volt DC input rather than an inverter.  Without additional loads the actual current draw is:

P............amp dry.......amp wet (humidity 4)
6 cm .....        0.7 .....           1.73
8 cm  .....        0.79 .....        2.00
10 cm .....      0.93  .....        2.30
12 cm  .....     1.06  .....         2.61
16 cm  .....     1.23  .....         2.33
20 cm   .....    1.66 .....          3.44

As you can see, even with the humidifier, and maximum pressure you can use a 42 a-hr battery and still have a 50% safety margin.  I think most of the above answers are including the inefficiency of an inverter, or assuming the AC power rating has a relation to DC power requirements.

I was looking at the Respironics 12V DC Battery Adapter Cable with Battery Clips Clips, along with the Shielded DC Cord for Dreamstation CPAP machines.  Will there be inefficiency, with those?  I understand that a lower pressure, causes less battery usage.  My pressures are 24/18, so obviously pretty high.  The back of the machine indicates that it is 12V, 6.67A, and 80W.  Based on what I'm reading, those are worst case scenarios?  I don't have a heated hose, just a standard hose, and a heated humidifier, which I typically keep on 4, but could lower it, in order to preserve battery life.
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The Respironics 12V DC Battery Adapter Cable is just a pair of conductors. IIRC, there are two EMI suppressors around the wires. The only inefficiency is the very small voltage drop along the wires. Bottom line, it's negligible.

I would go with Sleeprider's numbers. He researched those for you.

The back of the machine indicates that it is 12V, 6.67A, and 80W just means use a power supply capable of that. You'll note that 12V x 6.67 A = 80 Watts. The machine is intended for an 80 Watt supply. It does not mean it will draw 6.67 Amperes when running.

With your pressure and the humidifier on, you will be in the ballpark of 3.5 Amperes.

Mongo, member IEEE
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The numbers I posted are from Resmed which is based on a 12-24 volt up-converter The Philips power demands on straight 12 volt power are lower. The Philips numbers are frankly harder to come by, and out of pure laziness, I am giving the more conservative Resmed power requirements. I can tell you that users have gotten 2 to 2-1/2 nights in actual use, on a 32000 mili-amp hour li-ion battery on Philips CPAP and BiPAP units The most important feature is that the power supply or power bank has output of up to 3.75 amps at 12 volts, or the CPAP will shut down on startup. Once running, the units generally require less than 1-amp/hour. Your pressure range on bilevel may approach 1.5-2.0 amps.
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(05-12-2017, 03:50 PM)Sleeprider Wrote: Once running, the units generally require less than 1-amp/hour.  Your pressure range on bilevel may approach 1.5-2.0 amps.

Respectfully, amp/hour does not make sense.  I think you meant to say amp sans /hour.
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(05-12-2017, 01:51 PM)justMongo Wrote: The Respironics 12V DC Battery Adapter Cable is just a pair of conductors.  IIRC, there are two EMI suppressors around the wires.  The only inefficiency is the very small voltage drop along the wires.  Bottom line, it's negligible.

Two HONKIN BIG industrial grade nuclear strength suppressors.  Like the size of a frickin' C cell.

I made my own, without the suppressors.  

And in the words of Latka Gravis,"tinkyouvedddymuch."

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Overall, it seems like the general consensus is that 105AH will be more than adequate, along with the PR DC adapter and cord. I was able to find a relatively inexpensive charger, on Amazon. I'm going to go ahead, and get the stuff, and test it out, before my trip, so that I don't encounter any surprises.

Thanks again, to everyone, for your help!
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On a quick side note, does anyone know if there are any true dangers, with the deep cycle batteries? Are there any to avoid? Is there a danger to having one in my tent? Any precautions to take? I've heard that I should bring distilled water and make sure that it stay filled up. Is that correct?
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You should never recharge any acid filled battery in an enclosed space, regardless of if they are a sealed or non sealed battery- AGM or just old fashioned lead acid ones. 

If you have the battery on charge at night while using it to power the CPAP keep the battery outside the tent and just run the cord from the battery in to the tent. 

A sealed lead acid [SLA] or sealed acid gel mat [SAGM] battery should be ok to use inside the tent when it is not on charge, but still make sure you have adequate ventilation in case the battery seal is not perfect.
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The big danger is: Don't short the terminals. They can provide tremendous amounts of current.

While prudent to not charge in an enclosed area; a charger that does not exceed the gassing Voltage should not blow the vents open on a SLA/AGM.

remember the old VW Beetles (air cooled), their battery was under the rear seat. And it was a flooded, vented lead acid.

You should never need to add water to an SLA. There's no place to add it.
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Tbh I wouldn't even consider a 'wet' battery. If it is being fully charged it will bubble & gas. Not only would the smell of this be pretty unpleasant within the confines of a tent, it would also be potentially explosive. AGM batteries are commonly used within the confines of motorhomes & other RV's & are generally considered to be safe. I would have zero concerns about using one in a tent. They can gas (as has been said in a pevious post) in certain circumstances but the chances for this to occur if you use a reasonable quality multi stage charger with a float mode is extremely low & if you don't use a charger like that you will be wasting the money you spent on the battery as you will be unable to charge it to it's full capacity on a day to day basis, plus run the risk of overcharging it back home if/when left on charge for longer periods. Not only can overcharging prematuely kill a battery just as undercharging can, it can also lead to the circumstances where a Valve Regulated Lead Acid (VRLA) such as an AGM (Absorbed Glass Mat) or Gel battery *can* gas.
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