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Old 04-03-2013, 05:36 PM   #1
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More batteries

SMB Indiana put two Deka 8A27 92Ah AGM 12V batteries in my Sprinter van. I am finding this it not enough in the winter when we dry camp with the Espar furnace going all night and electric fridge. And with long nights we are more likely to use the TV in the evening. More lights use in the winter but all are LED. Running the generator and/or driving once a day is ok with us, but I am finding we are under 12V in the morning which is not good for the batteries.

The Sprinter has room for 1 or 2 more batteries in the engine compartment. SMB did not want to put one there for fear of warranty issues with the van computer etc. However, they said no problem if I wanted to install one there and I checked with Mercedes and they said the only issue is that if batteries were in the way they would have to charge me extra to remove them while they did maintenance. The van Engine control module is under where the batteries will go.

All my battery wiring so far is with 2/0 gauge welding cable and I will continue with that. I can wire the + side to the separator that is under the driver seat (I don't think I need an extra fuse for that). The - side I will have to run all the way to the back shunt if I want these batteries to be included in the battery monitor current readouts.

I need help deciding what to install. I see three options:

1. There is barely room to install two more of the identical batteries I have in the back. It will be a really tight squeeze. I have made some cardboard boxes the same size as the batteries and they fit. I am concerned it will be hard to remove them and they might rub against something to wear holes in them.

2. One of these batteries will fit nicely.

3. I could install two group 24 size batteries that are about an inch shorter and should fit pretty easily. I am concerned because I am told all batteries connected in parallel should be identical.

What I really want is two pair of 6V golf cart batteries. That is what I had in my former big trailer. I was surprised to find that SMB has to vent all batteries boxes and seal from the living quarters, even though they are sealed AGM batteries. Maybe when these batteries need replacing I will change over to golf cart batteries. Not sure if I can find ones that will fit. I think they will be safe in the vented enclosures.

Thanks for reading and let me know your thoughts on 1,2,3 and any other issues you see.

David
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Old 04-03-2013, 08:19 PM   #2
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Re: More batteries

I wouldn't bank different batteries (especially AGM and wet cells) together. Really a bank should contain all the same type, size, and age batteries. We do tie our starting batteries to the house batteries all the time, but they're usually separated by a charge relay of some type. Charging characteristics between different batteries and discharge ratings can pose problems with batteries directly tied together. Although it will work, most experts suggest the life of the batteries can be shortened. Myself I think it has more to do with the batteries when they discharge but I could be wrong.

With the advent of AGM's, 6 volt batteries aren't cracked up to what they used to be. You can read this in the newer info out there on many of the battery manufacture sites. There are 6 volt AGM batteries out there on the market but the construction is pretty much the same as their 12 v counterparts. In the end its up to you...good luck on your choice.
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Old 04-03-2013, 08:45 PM   #3
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Re: More batteries

Thanks Dave. If I changed to 6V wet cells I would do all 4 of them at the same time. I see now this would take a lot of research as things have changed since I had my trailer built 13 years ago, and will change more in the next 5 years before I need new ones.

My 2001 Ford 550 7.3L came with two different size batteries in parallel for engine starting...

For my Sprinter, I chose the AGM deep cycle starting battery option for the engine so when tied to the house batteries they would be the same type and size.

David
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Old 04-03-2013, 09:07 PM   #4
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Re: More batteries

Dave you might want to take a look at this sites FAQ's if you haven't yet. I'm sure there are other points of view though.
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Old 04-03-2013, 09:44 PM   #5
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Re: More batteries

A member on the forum has a short wheelbase Sprinter with Lithium ion batteries. They might be a nifty solution for some of us since they are lighter and dimensionally the same or smaller. I'm looking into a 300AH Lithium to replace a 200AH 4D.

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Old 04-03-2013, 10:22 PM   #6
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Re: More batteries

Bratworst --

Have you checked the price of those lithium deep cycle batteries? If not, sit down before you do...roughly $10 per amp hour, give or take -- for 300 ah capacity, you are looking at about $3K. Then you also need to make sure your charging system is regulated for lithium batteries -- they are selling them as "drop in" replacements, but I have also seen mention of needing charge controller tweaking or a "special lithium battery charger" to get the most out of them.

I was considering getting them until I saw the price -- just can't justify it.

That's at least six grand worth of batteries in that photo (over $7K at Smart Battery list price)!

Edited: this is from the Smart Battery FAQ regarding charging:

How do I charge a Lithium battery?
Smart Battery™ lithium ion technology uses the latest and most advanced built-in battery protection system to prevent damage to the battery. You may utilize a standard charger for our products, although in some cases a lithium charger may be required to charge the batteries.
Charging sources:
1.Alternator: Most alternators will sufficiently charge Smart Battery™ lithium ion technology
2.Inverter: Most inverters have a way to set or program the charging voltage. Lithium ion batteries need to be charged as close to 14.4v - 14.6v as possible to get a full charge.
3.Standard charger: A standard battery charger will charge Smart Battery™ lithium ion technology due to our advanced built in battery management system. 4.Lithium Charger: Purchase a Smart Charger from Smart Battery™ specifically designed to charge our lithium ion batteries up to 14.6V
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Old 04-04-2013, 03:02 AM   #7
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Re: More batteries

Regarding SMB venting and sealing the battery box/compartment, I believe this is due to RVIA building standards. Even if the van leaves the factory with AGM batteries, they have no way of knowing what type of batteries will be installed in the future.

My van (1998) had two house batteries, each in a big, clunky plastic battery box with vent tubes and whatnot. Took up a ton of room under the dinette seat. I installed AGM batteries and took out the plastic boxes, redoing under the bench to easily fit three AGMs in the less space than the two plastic boxes took.
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Old 04-04-2013, 06:25 PM   #8
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Re: More batteries

I ran afoul of that venting/RVIA issue too. But on the other hand, I have heard that AGM sealed batteries can vent a bit, but at such low levels as to be used on planes and such. And they don't heat as much so even more better (and I swear mine last longer, maybe cuz they're more robust, and maybe cuz they resist vibration damage). I am gonna take out the boxes and vents next time I replace them and just leave trays.

Regarding your plans, I'd be inclined to think two batteries of different size-type might have the same internal cell structure and therefore charging characteristics, so they'd work in parallel. But I'd check. Modifying the engine compartment and running the necessary cabling seems to be a bigger hassle, and maybe expense, than modifying the back. Those golf cart batteries are hard to wrestle around; a bank of smaller ones might be easier to deal with. I don't know where they put them in a Sprinter (mine are in a Ford under the gaucho).

BTW, I am doing some rewiring and found a nice source for cable covers, bus bars, and whatnot. I've been getting them at marine places and it was spendy; I got wind of vtewarehouse.com from pirate4x4; they sell really nice 4x 3/8" bus bars with covers for about $7 (they even have smaller screws for smaller gauges; nice touch). Prompt shipping too. And a lot of different kinds of terminal covers for crowded battery posts. They don't have great pictures on their website, so here's a couple.






You can just see the tops of the smaller screws in the bottom picture.

Good luck with the project.
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Old 04-05-2013, 08:54 AM   #9
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More batteries

Hey guys,

That battery box is mine and is wayyyy overkill but works like a charm. They are lithium iron phosphate not lithium ion like the smoldering Dreamliner ones. The overall cost with custom solar charger was 5k on sale any only required a 14.6v charge regulator and big ass 2/0 triple crimped wiring. I charge them using a secondary 360amp alternator and 400watts of solar. I have no genny, never plug in, and dry camp for days despite high load induction stove, 5cf fridge, microwave, killer av, lights, computer, welding and charging, shortwave, and heavy espar or danhard use in this mobile officeIt was spendy but has been awesome for dry camping and emergency operations! When you amortize the cost over 5 or more years then it makes sense financially too. A big up front investment no doubt but there is a projected saving because this huge bank rarely drops below 92 percent state of charge prolonging their life.

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Old 04-05-2013, 09:37 AM   #10
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Re: More batteries

So I don't know what AH battery those are but they look like this make:



This 100Ah battery cost 1300 bucks.
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