Foo - Questions about using a battery as a power supply.

First I am using a deep cycle marine battery as a power supply when I camp & there is no electrical hook up. I have to do this because I use a CPAP to sleep at night. I have used this battery for a total of 3 nights straight with out recharging it & got a full 8 hours sleep each night.

I connect the battery to a power inverter & plug the CPAP into the inverter.

This year I am doing the whole week of RAGBRAI. I will be using the battery for a total of 8 hrs a night for 7 nights to power the CPAP. Because of this I am testing to see if it will last that long.

I also have a queen size air mattress I was going to use that uses an electric pump to fill it with air. I tried to see if the battery would operate the pump to inflate & deflate the mattress. After one inflation/deflation it was pretty much out of power. So I decided on a self inflating camp pad instead.

When the battery ran out of power after using the pump I put the charger on it & recharged almost right away. So my first question is why is that?

Also the mattress pump operates at 0.9 A. I do not know how much is required to get it up to speed, or the max amps, but I am guessing the 0.9 A is the continues running power.

The CPAP requires a max of 1.0 Amps to get up to speed, then levels off. I do not know what the continuous operating power requirment is, my guess is much less.

Right now I am running the CPAP off of the battery with out me using it. So it is just blowing air out of the mask. I will also test it with me using it as well. Because of my breathing there may be a differance in power consumption to keep the CPAP operating at the required level. So far the battery is going strong as expected. After tonight it will have power the CPAP for a total of about 3 hours, with many more to go.

Why is it the battery has no problem operating my CPAP, but runs out of power when operating the mattress pump?

Thank you.

Power demand will be higher when you put on the mask due to the increase in ambient pressure and airflow impedance.

q. what does a power supply do?

a. it supplys power

How many volts is the pump rated for? I am guessing your deep cycle marine battery is 12v output?
If you had a 24v motor, and ran it at only 12v, it would draw more amperage than at the 24v. Also, electric motors pull a large amount of current to begin because they are not generating any back emf at a stand still. If you had a 12v motor with 1ohm of resistance, started it from a stand still with no soft start or anything, it would pull 12amps right away.

NC, my husband was on BiPap 24/7 and we used three 31Ah rechargable deep-cycle batteries for backup in the event of a power failure (and kept one on the wheelchair for whenever we weren't near and A/C line supply). He also used a humidifier, so we got a 600W pure sine-wave inverter.

What size battery do you have? What make is your Cpap? And at what pressure do you run it? Do you also use a humidifier? And, the most important question, how life-threatening is it if it cuts out? I assume you can always just sit up if necessary, even if you don't sleep?

When you're testing to see how long your battery will last, why not use it at home, in the manner in which it will be used while camping? This would be a better experiment since you will be drawing power for 8 hours, then not, then drawing power for another 8 hours, etc., and, the resulting increased occlusion of the air tube when the mask is actually on your face is important.

The pump for the mattress is probably is a high-volume flowrate pump drawing a lot of current. Check the specs on the motor, and tell me what it says.

How many volts is the pump rated for? I am guessing your deep cycle marine battery is 12v output?
If you had a 24v motor, and ran it at only 12v, it would draw more amperage than at the 24v. Also, electric motors pull a large amount of current to begin because they are not generating any back emf at a stand still. If you had a 12v motor with 1ohm of resistance, started it from a stand still with no soft start or anything, it would pull 12amps right away.

The mattress pump is rated at 120V. Yes the battery is 12V.

The inverter is a 200W, input of 12.8V DC 20A, with an output if 115V AC & powers up to 1.74 Amps.

NC, my husband was on BiPap 24/7 and we used three 31Ah rechargable deep-cycle batteries for backup in the event of a power failure (and kept one on the wheelchair for whenever we weren't near and A/C line supply). He also used a humidifier, so we got a 600W pure sine-wave inverter.

What size battery do you have? What make is your Cpap? And at what pressure do you run it? Do you also use a humidifier? And, the most important question, how life-threatening is it if it cuts out? I assume you can always just sit up if necessary, even if you don't sleep?

When you're testing to see how long your battery will last, why not use it at home, in the manner in which it will be used while camping? This would be a better experiment since you will be drawing power for 8 hours, then not, then drawing power for another 8 hours, etc., and, the resulting increased occlusion of the air tube when the mask is actually on your face is important.

The pump for the mattress is probably is a high-volume flowrate pump drawing a lot of current. Check the specs on the motor, and tell me what it says.

My CPAP is a Respironics Remstar Pro. I have had the machine for 3 years 2 months & 20 days now.

The battery is a Wal-Mart Ever Start made by Excide, deep cycle marine battery. I bought the biggest one I could about a year and a half ago. Heavy ass thing.

I am going to use it at home in the same manner I will use it camping. But I need to wait until warms up first. If the battery puts of fumes I want it outside the bed room window. Plus when I use it it will be outside the tent in the heat & humidity & not pulled into the machine & into to my lungs.

The mattress pump is 120V AC, 0.9A

For some the voltage on my CPAP is 100V to 240V. I'm guessing it operates somewhere in that range & levels out as needed when I am using it.

Like I said I have used it for 3 straight nights for 8 hrs each night. Worked fine. But I will be increasing that by 4 more nights.

My CPAP is a Respironics Remstar Pro. I have had the machine for 3 years 2 months & 20 days now.
Let me see what I can find out about your device online.

The battery is a Wal-Mart Ever Start made by Excide, deep cycle marine battery. I bought the biggest one I could about a year and a half ago. Heavy ass thing.Does it have an Amp-hour rating? Like maybe 31A-hr? If it's on the order of 25lbs, give or take a couple of pounds, that's what I'd guess.


I am going to use it at home in the same manner I will use it camping. But I need to wait until warms up first. If the battery puts of fumes I want it outside the bed room window. Plus when I use it it will be outside the tent in the heat & humidity & not pulled into the machine & into to my lungs.We went to "Batteries Plus" and bought three 31A-hr gel batteries, non-spillable, sealed, perfect for use indoors. The folks at "Batteries Plus" know what to show you if you say you need to use it for CPAP. I seem to recall that they were about $80 each, but I could be wrong about that.


The mattress pump is 120V AC, 0.9A How long does it take to inflate? That's not a very large curent draw. Is the battery also required for deflation?


For some the voltage on my CPAP is 100V to 240V. I'm guessing it operates somewhere in that range & levels out as needed when I am using it.The dual voltage specification just means that you can use it in the U.S. on 110-120V lines, or in Europe, where line voltages are 220-240V. What is your operating air pressure? How many cmH20? Your pressure requirement will have an effect on how much current the device will draw. The higher the pressure you need, the faster your battery will draw down.


Like I said I have used it for 3 straight nights for 8 hrs each night. Worked fine. But I will be increasing that by 4 more nights.Generally, once the battery voltage approaches 10V, higher-dollar inverters will sound an alarm. Once voltage drops below 10V, the inverter will shut out to protect the battery. What kind of inverter do you have? And do you have a cigarette lighter adapter with it?

mmkay. I found your manual: http://global.respironics.com/UserGuides/UserGuideREMstarPro.pdf

And the manual for the Respironics DC Battery Adaptor Cable: http://global.respironics.com/ServiceManuals/ServiceDCBatteryCables.pdf

According to your manual, your DCA max is 3.0A. According to the Cable manual, if you have purchased a deep-cycle battery, you can expect it to last up to 32 hours for any pressure setting. It doesn't say explicitly, but I would guess that this number is based on use of the Remstar Pro alone, without the optional humidifier. So, if you do use the optional humidifier, you can expect a considerable drop in the number of hours you can run your device.

You did not say what size your battery is, but I'm gonna have to say that you probably need to have two 100A-hr batteries to ensure that you will get eight 8-hour nights. Or, whatever combination of lower A-hr batteries will give you approximately 200A-hrs. You'll definitely want that safety factor of the extra day in there. Of course, there's always your car battery in a pinch, if you have the cigarette lighter adapter.

Sorry if this seems rather cumbersome. Hopefully, you have a car or truck in which you can leave the batteries, such that they won't get hot.

Hope this helps a bit. I'd recommend going somewhere like "Batteries Plus" and talking with them about your needs. Also, check out some of the online CPAP forums. I remember coming across a lot of threads a few years ago about people camping out and using their CPAPS on batteries, etc....

Good luck, and have fun! :)

mmkay. I found your manual: http://global.respironics.com/UserGuides/UserGuideREMstarPro.pdf

And the manual for the Respironics DC Battery Adaptor Cable: http://global.respironics.com/ServiceManuals/ServiceDCBatteryCables.pdf

According to your manual, your DCA max is 3.0A. According to the Cable manual, if you have purchased a deep-cycle battery, you can expect it to last up to 32 hours for any pressure setting. It doesn't say explicitly, but I would guess that this number is based on use of the Remstar Pro alone, without the optional humidifier. So, if you do use the optional humidifier, you can expect a considerable drop in the number of hours you can run your device.

You did not say what size your battery is, but I'm gonna have to say that you probably need to have two 100A-hr batteries to ensure that you will get eight 8-hour nights. Or, whatever combination of lower A-hr batteries will give you approximately 200A-hrs. You'll definitely want that safety factor of the extra day in there. Of course, there's always your car battery in a pinch, if you have the cigarette lighter adapter.

Sorry if this seems rather cumbersome. Hopefully, you have a car or truck in which you can leave the batteries, such that they won't get hot.

Hope this helps a bit. I'd recommend going somewhere like "Batteries Plus" and talking with them about your needs. Also, check out some of the online CPAP forums. I remember coming across a lot of threads a few years ago about people camping out and using their CPAPS on batteries, etc....

Good luck, and have fun! :)

If you mean physical size of my battery it is about: 7" wide, 13" long & 9" tall, it weighs almost 60 pounds, like I said, heavy ass thing. I do not know the amp hours on it. Because of it's size is the amp hours more then double then that of a smaller 25 pound battery? Say instead of 32 hrs, closer to 64 hrs? To easily carry the battery I have it in a plastic battery box designed for marine batteries.

My inverter sounds an alarm when the battery is getting low. That is who I knew it would not handle filling up the air mattress, the alarm went off.

I do not have the humidifier for my CPAP. My CPAP is set at 13 for the pressure setting. My apnea is pretty bad. I do have but never use the ramp feature on my machine, don't like to.

The inverter is connected to the battery with the "alligator" style clamps to the female end of a DC "cigarette" lighter end, the male end of the "cigarette" lighter plug is connected to the inverter, kind of like the pic on page 1 of this link: http://global.respironics.com/ServiceManuals/ServiceDCBatteryCables.pdf I use the CPAP AC power cord to connect to the inverter. Part of the cord on the clamp end is under the battery box lid, where it comes out I have going through a pvc plastic pipe with silicon sealing the end toward the female cigaretter lighter end, which goes through the power cord flap on my tent. The male connects to it, then to the inverter, etc. I will have to take & post pics of my set up.

If you mean physical size of my battery it is about: 7" wide, 13" long & 9" tall, it weighs almost 60 pounds, like I said, heavy ass thing. I do not know the amp hours on it. Because of it's size is the amp hours more then double then that of a smaller 25 pound battery? Say instead of 32 hrs, closer to 64 hrs? To easily carry the battery I have it in a plastic battery box designed for marine batteries.

My inverter sounds an alarm when the battery is getting low. That is who I knew it would not handle filling up the air mattress, the alarm went off.

I do not have the humidifier for my CPAP. My CPAP is set at 13 for the pressure setting. My apnea is pretty bad. I do have but never use the ramp feature on my machine, don't like to.

The inverter is connected to the battery with the "alligator" style clamps to the female end of a DC "cigarette" lighter end, the male end of the "cigarette" lighter plug is connected to the inverter, kind of like the pic on page 1 of this link: http://global.respironics.com/ServiceManuals/ServiceDCBatteryCables.pdf I use the CPAP AC power cord to connect to the inverter. Part of the cord on the clamp end is under the battery box lid, where it comes out I have going through a pvc plastic pipe with silicon sealing the end toward the female cigaretter lighter end, which goes through the power cord flap on my tent. The male connects to it, then to the inverter, etc. I will have to take & post pics of my set up.
When I say "size" I mean what amount of charge will your battery hold, in amp-hours? This is crucial for you to know. You can't assume by weight or physical size. Also, I can't tell from the Exide site if your battery is a pure deep-cycle battery or is a dual starting/deep-cycle battery based on the information I have. Ideally, you want the former for this purpose. You also want a sealed gel battery that's safe for use in enclosed spaces.

Here is the contact info for the Sioux City Batteries Plus store http://www.batteriesplus.com/store_details/129.aspx. I strongly recommend that you visit them, tell them you need a deep-cycle battery (or batteries) for running a CPAP, and tell them how many hours you need it to run, plus 20% for a little extra time cushion. Show them this: http://global.respironics.com/ServiceManuals/ServiceDCBatteryCables.pdf . They will be able to set you up with what you need. You might also tell them what battery you currently have to see about the possibility of using it, and buying whatever sealed gel batteries you need to ensure enough charge to run the CPAP for the whole week.

I think talking to someone local would be the best and safest route at this point. Hope this helped a bit! :)

I called Exide, the company that manufactured the battery for Wal-Mart to ask what the amp hours are. Wal-Mart for some reason did not want the amp hours labeled on the battery. I gave the part number to the person I talked with & the amp hours on my battery is 115 ah. This should be more then plenty to operate my CPAP for 7 nights, 8 hrs a night.

Careful there. Check the chart again: http://global.respironics.com/ServiceManuals/ServiceDCBatteryCables.pdf

You can expect 32 hours of battery service for a 100A-hr battery, which only gives you four 8-hour nights. I'm afraid you'll need two batteries of the type you already have. I hope you'll have access to a car, where you can keep the second battery, and then switch it out after that fourth night....

Again, might want to pick the brains of the folks at Batteries Plus. Maybe they have some better ideas to ensure that you won't end up havin' to sit against a tree trunk to sleep. :eek: <serious Vega look>

Careful there. Check the chart again: http://global.respironics.com/ServiceManuals/ServiceDCBatteryCables.pdf

You can expect 32 hours of battery service for a 100A-hr battery, which only gives you four 8-hour nights. I'm afraid you'll need two batteries of the type you already have. I hope you'll have access to a car, where you can keep the second battery, and then switch it out after that fourth night....

Again, might want to pick the brains of the folks at Batteries Plus. Maybe they have some better ideas to ensure that you won't end up havin' to sit against a tree trunk to sleep. :eek: <serious Vega look>

Because I am using the inverter so I can use it as AC vs DC power it is only drawing 1 amp, not 3 as it would with DC.

Because I am using the inverter so I can use it as AC vs DC power it is only drawing 1 amp, not 3 as it would with DC.You also have to account for the current used by the inverter to convert the DC to AC. Most manufacturers will tell you to figure .5 amp for the inverter. However I've seen some use more.

Is there going to be support on this tour? I'm assuming that you are not packing the c-pap and battery on your bike. Would a small generator suffice? I've seen them at the $250 price point.

Very good luck on what sounds like a fantastic tour.

Is there going to be support on this tour? I'm assuming that you are not packing the c-pap and battery on your bike. Would a small generator suffice? I've seen them at the $250 price point.

Very good luck on what sounds like a fantastic tour.


I am going with my bike club. We rent to trucks to sag the gear. Generators are a no, no. No matter how silent they claim to be, they are not quiet enough. Plus they require gas to operate, not a good idea to haul a generator filled with gas in a sag truck with luggage.

What I am doing starting tonight is sleeping with the CPAP powered by the battery. The machine has a counter of how many hours it has been used. I will see if I can get the equalivlent of 7 nights for 8 hrs a night. If not, I'll see how many hours it lasted & figure out what to do from there.

If the battery does not last all 7 nights for 8 hrs a night & depending on how much more I need I have some ideas on what I will do.

BTW, I have hauled the CPAP on my bike before. Last year when RAGBRAI started in Sgt Bluff I slept in my own bed. Sioux City & Sgt Bluff are 5 min., if that, apart. Because my gear was already on the sag truck on it's way to the first over night town & I had to use the CPAP when I slept at home I had to haul it on my bike. It does have a padded bag it goes in for transport. I secured it to my rear rack on my bike & carried it for 75 miles or so to Ida Grove.

If you have a support vehicle then you already have a generator. Just plug the battery and a DC to DC charger into the 12 volt Sssshhh! the cigarette lighter) outlet in the vehicle.

If you have a support vehicle then you already have a generator. Just plug the battery and a DC to DC charger into the 12 volt Sssshhh! the cigarette lighter) outlet in the vehicle.


The problem with that is unless the vehicle is running it will drain the battery & the truck will not be able to start the next morning. Or are you talking about doing this when the truck is being driven from town to town? That may work if that is the case.

And it is one option I may pursue depending on the out come of my testing how long the battery will last beyond 3 nights.

Need some sealed lead acid 26AH batteries? I have eight.

It is not a matter of 7 nights for 8 hrs each night, but more a total of 56 hours. There may be some nights on RAGBRAI I only sleep 7 & others I sleep 8.5 to 9.

Need some sealed lead acid 26AH batteries? I have eight.

How big are they? How much do they weigh?

N_C, why not recharge the battery in the SAG during the day? There are lighter plug to battery post clamp hookups with amperage limiters on them you do a nice slow trickle charge.....Why not utilize the SAG's charging system?:D

8 hrs of trickle charge on a deep cycle battery puts a substantial number of amp/hrs in a deep cycle battery! Keep the battery in a boat battery box while you are charging it so there's no risk of acid spill in the SAG, by the way!

N_C, why not recharge the battery in the SAG during the day? There are lighter plug to battery post clamp hookups with amperage limiters on them you do a nice slow trickle charge.....Why not utilize the SAG's charging system?:D

8 hrs of trickle charge on a deep cycle battery puts a substantial number of amp/hrs in a deep cycle battery! Keep the battery in a boat battery box while you are charging it so there's no risk of acid spill in the SAG, by the way!

Like I said it is a possible option pending the outcome of me using it to power the CPAP prior to RAGBRAI, which is what I am doing now. The battery has been stored & is carried in a plastic boat battery box since I have had it. The box has a lid that keeps rain, etc. off & it has 2 hand holds on the neds to carry it. The battery has a carry handle, but the damn thing weighs 60 pounds. Much easier to carry it from the hand holds on the box then the carry handle on the battery.

Other options I have is depending on how long the deep cycle battery I have lasts I can purchase a second smaller battery that will last the remaining time I will need it for & keep it stored in my rubber maid container I use for my clothing, etc. Another option is I have seen rechargable electric generators that provide something like 25 Ah that I can use as a power supply.

We are only allowed 2 containers in the sag truck for RAGBRAI. One is my large rubber maid container with 99% of my belongings inside of or strapped to the top of it I strap my tent & camp pad to the top & every thing else minus the battery is inside. The 2nd container is the battery. The battery is to heavy to put in the container. A smaller one would be fine, but not one that weights 60 pounds.

Because sleep apnea, this is why I need the CPAP, is not a disability the club is not required to make accomidations for me to have more then 2 containers on the sag truck. If it did qualify under the Americans with Disabilities Act, then they may have to comply & at best I would only need one additional container for a total of 3. And no I do not think sleep apnea should qualify under the disabilites act. It is something easily controlled & treated with surgery &/or a CPAP.

So far I have used the deep cycle marine battery for a total of 28.2 hrs to operate my CPAP. This is just over half of the 56 hrs I need it to last for. It is also 4.2 hrs over the lenght of time I have used it for in the past. In the past I have only used it for 3 nights in a row, 8 hrs a night for a total of 24 hrs.

What I may do now since I am at half of 56 hrs is take it to a battery place that is open today & have them test it to see how much of a charge is left on it.

So now I am getting into using it beyond what I had in the past so I'll see what happens & how much longer it will last.

I'll let you know & if it does not last up to 56 hrs I'll let you know what I'm going to do.

Not being a math whiz I do have a question. If the battery does not last for the full 56 hrs to figure out the amps drawn per hour by the CPAP, what figure do I take the time the battery did last for & divide it against? In other words lets say the battery only last for 40 hrs. What figure do I divide 40 into or against to figure out the amps drawn per hour so I can determine how much more I will need to last the remaining 16 hrs?

The battery lasted for 35 hrs. I need an additional 21 hrs. I either need a power supply that will last for at least 22 am hrs or a new battery that will last a total of at least 140 am hrs. I'll see if I can find one.

The battery lasted for 35 hrs. I need an additional 21 hrs. I either need a power supply that will last for at least 22 am hrs or a new battery that will last a total of at least 140 am hrs. I'll see if I can find one.
Why don't you use the SAG wagons charging system to recharge the battery in transit?

Like I said it is a possible option pending the outcome of me using it to power the CPAP prior to RAGBRAI, which is what I am doing now. The battery has been stored & is carried in a plastic boat battery box since I have had it. The box has a lid that keeps rain, etc. off & it has 2 hand holds on the neds to carry it. The battery has a carry handle, but the damn thing weighs 60 pounds. Much easier to carry it from the hand holds on the box then the carry handle on the battery.

Other options I have is depending on how long the deep cycle battery I have lasts I can purchase a second smaller battery that will last the remaining time I will need it for & keep it stored in my rubber maid container I use for my clothing, etc. Another option is I have seen rechargable electric generators that provide something like 25 Ah that I can use as a power supply.

We are only allowed 2 containers in the sag truck for RAGBRAI. One is my large rubber maid container with 99% of my belongings inside of or strapped to the top of it I strap my tent & camp pad to the top & every thing else minus the battery is inside. The 2nd container is the battery. The battery is to heavy to put in the container. A smaller one would be fine, but not one that weights 60 pounds.

Because sleep apnea, this is why I need the CPAP, is not a disability the club is not required to make accomidations for me to have more then 2 containers on the sag truck. If it did qualify under the Americans with Disabilities Act, then they may have to comply & at best I would only need one additional container for a total of 3. And no I do not think sleep apnea should qualify under the disabilites act. It is something easily controlled & treated with surgery &/or a CPAP.
And Physical disabilities can be easily treated by use of items like wheelchairs. Apnea does count as a disability under the ADA. This was established by a law suit involving the transportation industry. A Commercial carrier tried to ban CPAP use by their drivers or plugging them in to the electrical system. They were ordered to make accommodation in their trucks by a federal judge. CPAP is considered "Lifesaving Respiratory Equipment" and covered under accommodation laws. Without it you CAN die.

Why don't you use the SAG wagons charging system to recharge the battery in transit?

That is one possibility. I will talk with the RAGBRAI coordinator about it. If I am not mistaken the power to the pwoer outlet.cigarette lighter is only there when the vehicle is turned on & running, so it is not taken from the vehicle battery. So I could laod the battery into the cab on the floor, connect the charger to it & the cigarette lighter outlet. When the vehicle is started it will start chagring & when it is shut off it will stop. I think this is the way it works. Correct me if I'm wrong.

That is one possibility. I will talk with the RAGBRAI coordinator about it. If I am not mistaken the power to the pwoer outlet.cigarette lighter is only there when the vehicle is turned on & running, so it is not taken from the vehicle battery. So I could laod the battery into the cab on the floor, connect the charger to it & the cigarette lighter outlet. When the vehicle is started it will start chagring & when it is shut off it will stop. I think this is the way it works. Correct me if I'm wrong.
Lighter outlet is always on.

Lighter outlet is always on.

So I'll have to ask the driver to plug the charger in after he turns on the engine, this way it is not drawing from the vehicle battery which can potentially drain it. Or does the lighter outlet only draw from the battery & does not switch over to drawing from the alternator power after the engine is started?

If the truck has another power outlet other then the cigarette lighter does it draw from the battery only, the alternator only or both, the battery when it is off & the alternator when the engine is on.

So I'll have to ask the driver to plug the charger in after he turns on the engine, this way it is not drawing from the vehicle battery which can potentially drain it. Or does the lighter outlet only draw from the battery & does not switch over to drawing from the alternator power after the engine is started?

If the truck has another power outlet other then the cigarette lighter does it draw from the battery only, the alternator only or both, the battery when it is off & the alternator when the engine is on.
If the engine is off, the charging will have to be interrupted to prevent drawdown of the truck battery.

I sent an email to the RAGBRAI Coordinator asking if it is ok to use the cigarette lighter power port in the rental truck to charge the battery between the over night towns on RAGBRAI. I would only need to do this a total of 3 times during RAGBRAI. If he says it is not ok then it is on to plan B. Which is a second smaller battery with enough amp hours to last the rest of the trip.

How do you connect both batteries together so the CPAP is drawing power from them? Or when one is drained it automatically starts drawing from the other? Or is this not a good idea?

I sent an email to the RAGBRAI Coordinator asking if it is ok to use the cigarette lighter power port in the rental truck to charge the battery between the over night towns on RAGBRAI. I would only need to do this a total of 3 times during RAGBRAI. If he says it is not ok then it is on to plan B. Which is a second smaller battery with enough amp hours to last the rest of the trip.

How do you connect both batteries together so the CPAP is drawing power from them? Or when one is drained it automatically starts drawing from the other? Or is this not a good idea?
PC2 would be better for this question. Lets see......Parallel hookup of 2 batteries = same voltage and greater stored capacity. Make sure you don't hook up in series, or you'll get 24 volts!
http://sierranevadaairstreams.org/owners-guide/understanding/battery-config.html

How big are they? How much do they weigh?

rough estimate, they're about 8" x 8" x 6" and weigh a good bit. I haven't load tested these, so I don't know which ones are good.

I sent an email to the RAGBRAI Coordinator asking if it is ok to use the cigarette lighter power port in the rental truck to charge the battery between the over night towns on RAGBRAI. I would only need to do this a total of 3 times during RAGBRAI. If he says it is not ok then it is on to plan B. Which is a second smaller battery with enough amp hours to last the rest of the trip.

How do you connect both batteries together so the CPAP is drawing power from them? Or when one is drained it automatically starts drawing from the other? Or is this not a good idea?
By the way, parallel will draw from both batteries simultaneously, they'll share the load rather than draw one down and then switch to the other. Simultaneous draw will be a simpler system than setting up a switching system, no switches or control heads that way as well as no vampiring of stored power to operate the switch, or impedance loss either.:D

So I'll have to ask the driver to plug the charger in after he turns on the engine, this way it is not drawing from the vehicle battery which can potentially drain it. Or does the lighter outlet only draw from the battery & does not switch over to drawing from the alternator power after the engine is started?

If the truck has another power outlet other then the cigarette lighter does it draw from the battery only, the alternator only or both, the battery when it is off & the alternator when the engine is on.
This doesn't matter, because if the alternator is driving juice, the battery is charged constantly at varying levels anyway. It also draws power off the battery to charge the coils of the alternator anyway. (Don't pull the cables to test a modern alternator doing the old "if it dies with the battery disconnected the alternator is bad test", it'll blow the alternator from a voltage spike! The battery is also a buffer/excess power sump!):eek:

To hook the batteries in parallel do I connect one to the other, then the inverter to one of the batteries & the CPAP to the inverter? Will have it set up in parallel cause it to last more then 35 hours before I run out of DC power?

To hook the batteries in parallel do I connect one to the other, then the inverter to one of the batteries & the CPAP to the inverter? Will have it set up in parallel cause it to last more then 35 hours before I run out of DC power?
Here's a simple diagram of parallel wiring for 12 V. It's the first one on the page. It's easier to show you than explain it.;)

Here's a simple diagram of parallel wiring for 12 V. It's the first one on the page. It's easier to show you than explain it.;)

pic or link?

Too tired now. I'll look at this thread tomorrow to see what jibes with what I know technically and experientially. When is RAGBRAI, N_C?

Too tired now. I'll look at this thread tomorrow to see what jibes with what I know technically and experientially. When is RAGBRAI, N_C?

The last full week of July.

mmkay. G'night. :)

I got a response back from the RAGBRAI Coordinator saying it is ok to do this. He stated if anyone asks, because there are some who may get jealous & want to do the same thing, we simply say it is medically needed, which it is. We won't make a big deal out if it to kind of keep it under wraps to help avoid this though.

I think one thing that helped my case with this is I offered to pay the drivers a few bucks for their trouble of plugging & unplugging it from the power port in the truck to keep it charged.

But I still want to know how to set up 2 batteries in parallel though.

pic or link?
Woops, sorry N_C I thought had put a link in, here it is!
http://www.solarray.com/TechGuides/WireDiagrams_T.php :D :eek:

Woops, sorry N_C I thought had put a link in, here it is!
http://www.solarray.com/TechGuides/WireDiagrams_T.php :D :eek:

Thanks. I take it the main is the power inverter or the CPAP machine, correct? If it is this will be really easy to do. From the inverter to the battery I use a positive & negative cable with the alligator type clamps. Using the jumpers from battery to battery could be a cable with a alligator type clamp on each end.

Thanks. I take it the main is the power inverter or the CPAP machine, correct? If it is this will be really easy to do. From the inverter to the battery I use a positive & negative cable with the alligator type clamps. Using the jumpers from battery to battery could be a cable with a alligator type clamp on each end.
Yep! Main out is to the inverter unless your CPAP can run on 12V as well. By the way, if you have problems with your inverter, Pilot and other truckstops carry them for about $40.00 for a 300 watt inverter if you have a burnout. Just a little fallback info for you!:D

Yep! Main out is to the inverter unless your CPAP can run on 12V as well. By the way, if you have problems with your inverter, Pilot and other truckstops carry them for about $40.00 for a 300 watt inverter if you have a burnout. Just a little fallback info for you!:D

It can run on 12V, but I'd rather not do that, for one I don't have the DC power cord for it.

On my battery & probably the second one, if I buy another & go this route, there will only be one set of battery posts. Because of this is it ok to connect the alligator clamps for both the positive & negative cables from the inverter & the jumpers to the same posts & have them touching?

Also as I said my battery is rated at 115 amp hrs, lets say the second one is 75 amp hrs. Does that mean I will have a total of 190 amp hrs with them being wired in parallel?

It can run on 12V, but I'd rather not do that, for one I don't have the DC power cord for it.

On my battery & probably the second one, if I buy another & go this route, there will only be one set of battery posts. Because of this is it ok to connect the alligator clamps for both the positive & negative cables from the inverter & the jumpers to the same posts & have them touching?

Also as I said my battery is rated at 115 amp hrs, lets say the second one is 75 amp hrs. Does that mean I will have a total of 190 amp hrs with them being wired in parallel?
Very close, there will be a small loss due to impedance issues, but not much (~.05%):D

Very close, there will be a small loss due to impedance issues, but not much (~.05%):D

Ok what about the clamps touching one another on the same posts? Will that be an issue?

BTW I am learning about how electronics work within the telecommunications industry. Still going through the course work for it & have not quite gotten to this part. I do what impedance is though. But have yet to learn about the series & parallel wiring.

Thanks for all the help.