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Discussion Starter #1
Is it possible to charge two batteries at once? I need to run my CPAP machine when I'm camping but a lithium CPAP battery costs $200-$300++. I'm wondering if I can just buy a second powersport battery @ Walmart for <$50 to run my CPAP overnight and then run a lead from my regular battery during the day to charge it back up. I could swap them out each morning but that would be a bit of a PIA if I can avoid it. Much easier just to carry the second battery in my pannier and run a lead from my battery tender lead but will this overload the charging system?
Any advice greatly appreciated.
 

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You would need to do it like the 4x4 and caravan guys do it. They put a switch in the system that isolates the second battery when the motor isn't running so that you can drain the aux battery without leaving yourself stranded, but also restrict the charging current to it so that the inrush into a dead battery doesn't overload the charging system. The electrics in these bikes are not overly sophisticated, and for normal bike use they don't need to be. That doesn't mean it's impossible, but it's a lot more expensive than just hooking a second battery up in parallel with the normal one.
You might be able to get a small charger than plugs into an aux socket, which would be the easiest solution that doesn't cause substantial fire risk.
 

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You can charge two at once it is just going to take twice as long. I have a CPAP too and camping I either run a honda 2000i generator or run an inverter from the car battery. A motorcycle battery isn't going to have enough juice to last the night. And make sure you turn your humidifier off on the CPAP or it will suck that battery empty in just a few hours. During the day I either run a charger from the generator, put a solar charger on it or drive.
 

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You can charge two at once it is just going to take twice as long. I have a CPAP too and camping I either run a honda 2000i generator or run an inverter from the car battery. A motorcycle battery isn't going to have enough juice to last the night. And make sure you turn your humidifier off on the CPAP or it will suck that battery empty in just a few hours. During the day I either run a charger from the generator, put a solar charger on it or drive.
You run your car or a generator ALL NIGHT when you're camping?
 

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One problem is a lead acid battery doesn't like being repeatedly run flat. If the CPAP is running it completely down it wont last long. A deep cycle battery would be better but I'm not sure they make small ones. You wont be charging two batteries as the bike battery will be fully charged less a start. Perhaps a small intelligent charger like a NOCO and a campground where you can plug it in somewhere would work better. Plug it in in the morning till you leave then finish charging it when you get to your next site.
 

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Thx but the second battery won't be connected except for charging. I'll carry it just to power my CPAP overnight and then charge it during the day as I ride
 

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You can charge two at once it is just going to take twice as long. I have a CPAP too and camping I either run a honda 2000i generator or run an inverter from the car battery. A motorcycle battery isn't going to have enough juice to last the night. And make sure you turn your humidifier off on the CPAP or it will suck that battery empty in just a few hours. During the day I either run a charger from the generator, put a solar charger on it or drive.
This is great, and similar to what I've tried for car camping, but for MC camping it's not practical. I don't mind how long it takes because when I'm on a MC camping trip I ride at least 6-8 hours a day - I just want to check to make sure it's not hard on the charhging system or the main battery
 

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One problem is a lead acid battery doesn't like being repeatedly run flat. If the CPAP is running it completely down it wont last long. A deep cycle battery would be better but I'm not sure they make small ones. You wont be charging two batteries as the bike battery will be fully charged less a start. Perhaps a small intelligent charger like a NOCO and a campground where you can plug it in somewhere would work better. Plug it in in the morning till you leave then finish charging it when you get to your next site.
Good advice but a lot of the state/FS campsites don't have power. My travel CPAP is really small and doesn't have a humidifier and I'm hoping I can get at least 6 hours out of a powersport battery. I can buy a battery at WM for <$50 and if it lasts for a week I'm OK with tossing it at the end of a seven-day trip. I'm just worried about charging it during the day as a second battery hooked up to my primary battery
 

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I have a co-worker that hated his CPAP machine. He found a dental alternative that works the same. From what he heard, its about a 50% chance it'll work for each person. The dentist does a custom fitting, then has the device built to your mouth. You put it in at night and it opens up your passage and he gets a full night's sleep. As an added bonus, it doesn't use any electricity and is much easier to clean/maintain. Might be a better alternative.

https://www.webmd.com/sleep-disorders/sleep-apnea/mouth-devices-for-sleep-apnea#1

Good luck!
 

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Yes, you could charge a second battery. Won't be harder on the charging system in any way I know of.

BUT...you MUST be careful. While the battery likely won't be fully discharged it will still be low. That means you will be moving quite a bit of current to it. Meaning you need to use heavier gauge wire than you might first think of using. Battery tender size wire won't cut it. Could overheat the wiring.


It is exceedingly rare for a dental appliance to actual reduce sleep apnea events to an acceptable level. If you are having trouble with cpap, there is help. Once you get it figured out, it isn't so bad. No need to be kept awake fighting the system or dealing with sore skin from masks. Go to your Doctor and likely their eyes will glaze over when asking about cpap help. They have automated responses and not much beyond that. If I had to use what was first brought to me ( at very high costs ) to use I probably would have not kept with it. Learn from others. Here is a CPAP Forum that is a good place to start. Or pm/e-mail me, I would be glad to help. The difference this makes in how you feel is worth the trouble to optimize the therapy so it works for you.
 

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The BMW RT-P, police model, I had did have 2 batteries. One was in the glove box in the fairing. It was the back up so that they could have the flashing lights and not run the bike all the time.
It's a straight forward matter and just requires proper separation to insure the bike battery doesn't get discharged. If I understand the need, you will have a second battery that is removed from the bike and installed in your cpap device for sleep. So it will fit in the saddle bag/top box for recharging when you are riding.
I can envision the set-up but lack the knowledge to lay it out properly for you.
Hopefully one of the smarter electrical types can send you a diagram of the necessary wiring.
 

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Like other said, in theory charging two batteries at once should not be a problem. (Just don't make a polarity mistake.)

In practice, you need to run the numbers. Your V-Strom, depending on the exact model and how many accessoires you're running, might only have 50-100W power available to charge that second battery. And that may only be available when running at, say 3000RPM or more, not at idle. Is that enough, across a 6-hour ride, to fully charge that depleted CPAP battery? What if your ride is cut short due to weather or other circumstances?

Also factor in some losses. Just charging and decharging alone you probably need to calculate with 20-30% loss, but if there's a voltage conversion in the solution somehow (e.g. from 12V to 110/220V and back to 12V), then your total loss might be more than 50%.

So, for starters, how many Ah do you need for your CPAP to get you through the night? (or: How many watts does your CPAP use?) And is this a standard 12V battery or does it use an odd voltage? Is it chargeable at 12 (actually 14 and a bit) volts, like from a cigarette lighter outlet, or do you need to charge it using a mains socket?
 

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Dale, I learned early on that my insurance company would not spring for a battery for the CPAP. They said it was not necessary equipment. I supposed I only needed to breath when the power was on. They had no comment. Motorcycle camping in remote areas has thus been put on hold for me until I figure it out. So I am interested in your battery charging solution. Please post your decision/results.

I have been considering a micro battery such as these.... https://shop.antigravitybatteries.com/productline/micro-starts/ Spendy, but my research is showing that the battery should survive more than one night of CPAP w/o charging. TBD.

In November 2018 I started a low carb, no sugar food plan and have dropped 30-35 pounds so far. I've been able to reduce the CPAP pressure from 11 constant down to 6 variable. Hoping that change reduces the nightly draw on a battery too.

Let us know your solution when you figure it out.
 

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I have been considering a micro battery such as these.... https://shop.antigravitybatteries.com/productline/micro-starts/ Spendy, but my research is showing that the battery should survive more than one night of CPAP w/o charging. TBD.
Those batteries will not work and could even be dangerous for that job.

They are built for a very high very short burst of power.

If they are pulled to far down you will risk a fire when trying to bring the charge back up.

If you read the instructions they are to be left on the battery that is to be helped for a few moments only, if they are left on too long a chemical reaction can start, one you can't stop.

When on charge do not turn your back on them.
 

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There are many ways to do this but none are cheap. (I don't really like getting involved in this because there are so many variables)

First you need to work out how much battery you will require to get through the night, I once tested a mates machine and it pulled 2.5amps you would need to test your machine and multiply that by the number of hours you want to use it then choose the appropriate battery for the job remembering the further you pull a battery down the more you damage it so the shorter the life of the battery, you should then test your system at home over a number of nights, a bad nights sleep could be life threatening.

The bigger the battery plates EG; deep cycle and the lower the voltage gets the more power required to bring the charge back up, to over come this a DC to DC charger is best, you can boost the amps going into the second battery the problem is a DC to DC can be expensive and take up a lot of room but the time required to recharge is shortened.

You could use a VSR (voltage sensing relay) with those you can set the open and close voltages, that way you can pull power from both the bikes battery and the second battery at the same time until the low voltage set point is reached then the batteries will separate, by doing that you reduce the size of the second battery but still leave enough power in the bike battery to start the bike, if you were to go down this path I would learn to start the bike without the headlights coming on. (I can explain if required) when you start the bike it will charge the starter battery first and that is good because the bikes battery will take a charge much quicker than a deep cycle battery (bike batteries produce power quickly and take a charge quickly)

You can just join the batteries together with very large cables and Anderson plugs but how satisfactory it is will depend on the ride time, the discharged state and type of second battery, I would recommend turning off one headlight or fitting LED globes to speed things up.

I if were me in your position and did not want to spend any money I would build a isolation switch into the system, you will still need to know the size of the second battery required but after staring the bike I would switch over to run the bike off the second battery and disconnect the bike battery, this will give the second battery all the available amps in hope of bringing the charge back up ASAP.
 

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I once tested a mates machine and it pulled 2.5amps
Based on this, some preliminary numbers.

If the CPAP indeed pulls an average 2.5A off a 12V battery (30W), you'll need a 20Ah 12V battery at least to get you through the night (8 hours). Make that 24Ah or even more if you want to have some reserve, and don't want to deep cycle the battery each day. So you'll end up with a fairly big battery - for comparison your VStrom battery is only 12 Ah.

Assuming your charging system has 100W available (and that's probably optimistic), recharging a 20Ah battery from scratch, in theory, takes a minimum of 2.4 hours. If you assume only 50W is available, 4.8 hours minimum theoretically. And that's not counting any losses due to inefficiency or a non-optimal charging method.

Also consider that the way you're using the battery is not optimal, so it may quickly become a heavy paperweight. It's not just the deep decharge each day, but you're also recharging at a more or less constant voltage, which is not the ideal/optimum way to recharge a battery.

So it looks like it's doable, but it's marginal. You'll probably have to ride for a minimum of about six hours per day to make the numbers work out. And the battery might be toast by the time your holiday is over. (Then again, lead-acid batteries of 24Ah are about 50-75 dollars, so you can just factor that into your holiday budget.)
 

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Cpap machine amperage draw is a LOT different across models. I run an HDM Z1 that draws less than my ResMed Airsense 10 Autoset. You absolutely cannot use a heated humidifier chamber for instance ( part of why some listed amperage will be high ).

ResMed Battery Guide will give you much of the information you are looking for.

As shown, many machines can operate under 1 amp hour load. I would read the guide linked to above to get straight information on amp draw and how to power your unit with battery.
 
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