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Old 09-27-2016, 09:56 PM   #1
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I need some battery education....

Mechanically, I'm always good to go, electrically, not so much. I want to add an additional battery to my camper. It has a deep cycle marine battery now (in a vented battery box). Can I replace it with an AGM and delete the battery box and add another AGM in parallel. I have room for another in a location about 3 feet from the original battery.

I sleep on a CPAP machine at night (running through a xantrex PSW inverter.) It's running on one group 24 battery now and lasts all night but I feel 2 would be better.

I recharge with an inverter genny everyday for 2 hours. Solar don't work, I camp in the woods all the time...

My big question is, does an AGM battery have to be vented to the outside and if so, what type of battery don't have to outside vent? Would be very hard to vent the second battery...

Or should I just upgrade the 24 to a 31?
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Old 09-27-2016, 10:11 PM   #2
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An AGM battery does not need to be vented. You should have no problems with running the two new AGM batteries in parallel. IMO a bigger battery is always preferable to a smaller one.
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Old 09-27-2016, 10:16 PM   #3
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An AGM battery does not need to be vented. You should have no problems with running the two new AGM batteries in parallel. IMO a bigger battery is always preferable to a smaller one.
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Old 09-27-2016, 11:00 PM   #4
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For a good 12v system education, Google "The 12 Volt Side of Life".
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Old 09-28-2016, 12:21 AM   #5
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Take the advice from "The 12 Volt Side Of Life" with a grain of salt. There are some statements made that are a bit far from accurate.
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Old 09-28-2016, 04:51 AM   #6
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If you are going going to run the batteries in parallel you will want to buy two new batteries so they are the same.
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Old 09-28-2016, 05:20 AM   #7
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Yes you can use AGM batteries without worrying about venting. As some of the other posts indicate, you need to install them in parallel, but when you do that it is best that both batteries be exactly the same model and age and the cable lengths to both should be identical. That is because in parallel it doesn't take a lot of difference for one battery to get the lion's share of the load and the recharge current. While this isn't totally the end of the world, the loaded and more used one will wear out much faster under those circumstances.
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Old 09-28-2016, 05:58 AM   #8
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I'm all for the extra battery. It's the first mod I make to every camper I have owned. Have you considered running directly off the battery? Inverters are only about 80% efficient. I also use a CPAP but with the 12v adaptor. I installed a 12v socket close to the night stand. We often stay off the grid too and used the generator to charge up the batteries.
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Old 09-28-2016, 06:26 AM   #9
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Yes 2 new batteries; the connecting wires between the batteries as large in diameter as available, exactly the same length, and as short as will fit; wire exactly as indicated for equal charge and discharge cycles.

Positive from camper on one battery and negative from camper on the other one.
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Old 09-28-2016, 06:37 AM   #10
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Quote:
Originally Posted by SidecarFlip View Post
Mechanically, I'm always good to go, electrically, not so much. I want to add an additional battery to my camper. It has a deep cycle marine battery now (in a vented battery box). Can I replace it with an AGM and delete the battery box and add another AGM in parallel. I have room for another in a location about 3 feet from the original battery.

I sleep on a CPAP machine at night (running through a xantrex PSW inverter.) It's running on one group 24 battery now and lasts all night but I feel 2 would be better.

I recharge with an inverter genny everyday for 2 hours. Solar don't work, I camp in the woods all the time...

My big question is, does an AGM battery have to be vented to the outside and if so, what type of battery don't have to outside vent? Would be very hard to vent the second battery...

Or should I just upgrade the 24 to a 31?
Here ya go.
The 12volt Side of Life (Part 1)
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Old 09-28-2016, 06:43 AM   #11
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Originally Posted by Mars View Post
I'm all for the extra battery. It's the first mod I make to every camper I have owned. Have you considered running directly off the battery? Inverters are only about 80% efficient. I also use a CPAP but with the 12v adaptor. I installed a 12v socket close to the night stand. We often stay off the grid too and used the generator to charge up the batteries.
My machine didn't come with an adapter so 110 is the only option (I use an older Res-Med unit). Some things never wear out.
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Old 09-28-2016, 06:52 AM   #12
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Originally Posted by SidecarFlip View Post
My machine didn't come with an adapter so 110 is the only option (I use an older Res-Med unit). Some things never wear out.
Those CPAP units are very low power users and inverters are a lot more efficient at low power demands (vs capacity). If you need a powered humidifier with yours consider one of the "un-powered" ones that route your air over a flat container of distilled water.

CPAP.com - REMstar Passover Humidifier with hose

We use a powered one that works great all night with dual 75AH DP batteries and a 1000Watt inverter.

CPAP.com - HC150 Heated Humidifier With Hose, 2 Chambers and Stand

You may also find the correct 12 volt cable for your unit here:
http://www.cpap.com/cpap-battery-pow...-dc-cables.php
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Old 09-28-2016, 07:00 AM   #13
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Like I said, mechanically, I'm fine. I farm so I fix and maintain all my equipment....Electrically, not so much.

The inverter install was seamless. I installed it very close to the battery that came in the unit and used welding cable and crimp / solder on lugs for the connections I bought an over rated Xantrex (3000 watt) when I knew I'd need much less (the CPAP machines is 75 running watts) 'in case' of future need and I hard wired the converter to one dedicated GFI outlet near the overcab bunk so I can 'plug in' but still have the outlet available for other stuff in the future.

The Xantrex is a remote on and off unit and it's efficiency rating is 93% not 80 like a cheap convertor (wasn't cheap)

If I remove the existing battery box and venting, I can get 2 group 24's side by side in almost the same space the box now occupies, not a bad deal. With a slide in TC, you want to keep 'dead' weight as far forward as possible anyway.

Thanks for all the replies, I appreciate any and all assistance.

My last question is (and lets not get into an oil like discussion if possible), what do you folks recommed for an AGM battery? Years ago, I used an Optima in another application with very mixed results. It was expensive and trally didn't work out very well. Are there other more viable options?
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Old 09-28-2016, 07:10 AM   #14
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I have VMax AGM and love them.

https://www.amazon.com/VMAX-MR127-Ma...+cycle+battery

If this one will fit and you can get by on 150AH in a single battery:

https://www.amazon.com/Vmaxtanks-VMA...+cycle+battery
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Old 09-28-2016, 07:39 AM   #15
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You might find that the efficiency of the inverter is more like 80% when you are only drawing 75 watts on a 3000 watt inverter. Generally the efficiency climbs to over 94% when you hit maybe 20% of the rated wattage of the unit.
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Old 09-28-2016, 12:44 PM   #16
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Batteries

You can also use 2 - 6 volt batteries in series. 6 volt agm golf cart batteries are widely available
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Old 09-28-2016, 01:54 PM   #17
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You can also use 2 - 6 volt batteries in series. 6 volt agm golf cart batteries are widely available
Yes, if you are going to follow the recommendation of replacing the original 12v battery so that you have two of like capacity, you are better to go with 6v batteries. Less space is wasted on insulators, so they have more capacity for any physical size.
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Old 09-28-2016, 02:31 PM   #18
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Hmmmm... This was an interesting topic. I, too, use a ResMed (110) CPAP machine, and one time I charged my 2 deep cycle interstate (24) batteries one night and then went to bed using the CPAP machine. About 2:00am I woke up to a beeping sound and the XanTrex inverter had a red light blinking on it. I checked the batteries and they had discharged to almost nothing. I did have my inverter attached to the batteries in parallel and had all cables the same length which was about 4 feet. (awg4 cable) Don't know what I did wrong, but haven't used CPAP since that first time. I am definitely not electrically inclined. :-(
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Old 09-28-2016, 02:44 PM   #19
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My machine didn't come with an adapter so 110 is the only option (I use an older Res-Med unit). Some things never wear out.
I have an older Res-Med unit too. I had it calibrated a few years ago and it still works great. I think many are actually 12v units. My 12v plug goes into my unit and straight to the 12v plug nothing inline. I keep that one in the camper.
My new one has heated hoses and all kinds of stuff. I figure it's a power hog but I have never tried it on the camper batteries.
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Old 09-28-2016, 03:49 PM   #20
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You might find that the efficiency of the inverter is more like 80% when you are only drawing 75 watts on a 3000 watt inverter. Generally the efficiency climbs to over 94% when you hit maybe 20% of the rated wattage of the unit.
So the more demand the more efficient?
I had believed it was the opposite. Thanks.
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