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Odyssey 6TL Battery Mounting Question. Anyone tried swapping to 8D AGM batteries?

exon111

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OC, CA
I recently bought a 2012 MTV 6x6 on consignment at an expedition RV builder in MO. The batteries are toast and need to be replaced. The truck is currently at the RV builder pending the start of an RV build with them.

They just quoted me 3 to 4 hours of labor plus parts to replace the batteries. The stated reason for why they quoted 4 hours labor to replace batteries is because the original Fiamm AGM batteries are no longer available, and the only replacement option is orange Odyssey 6TL AGMs. They say it will take several hours of battery tray modifications to mount the Odyssey 6TL batteries. Aren't 6TL batteries all the same size? Can anyone who has replaced their 6TL batteries confirm if this is a real issue? This explanation just seems a little odd to me and I want to fact check it. If what they are saying about this is incorrect, I'm afraid of what other issues will crop up while starting a very $$$ and complex build with them.

The second question I have is whether it's feasible to replace the 4 original 6TL batteries with two 8D AGM batteries, such as those offered by Lifeline. Two 8D batteries offer the exact same capacity as four 6TLs and cost quite a bit less. Dimensions of an 8D are pretty similar to two 6TLs. I figured if we are going to be stuck modifying the battery tray anyway, might as well save some money in the long run by converting over to 8Ds. Anyway, when I proposed this, the RV builder's electrician says he doesn't think this is possible because the truck has 24v and 12v electrical systems. I'm no electrician, but can't you wire two 12v batteries both in series and in parallel to give you both 12v and 24v? If I know more than their electrician that's a bit scary, but this is definitiely not my field of expertise so maybe they are right. They have built at least 10 RVs on FMTVs so I would expect them to know the platform pretty well.

What do you guys think? I'm not so much concerned about a few hours extra labor in the overall scope of a large RV build, rather I want to make sure these people actually know what they are talking about and are not BSing me.
 
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exon111

Member
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Location
OC, CA
Man this forum is great. While googling series parallel wiring in general, I was brought back to a Steelsoldiers thread which seems to answer my second question. Looks like you can't wire two 12v batteries both in series and parallel so the electrician is apparently right on that point. https://www.steelsoldiers.com/showt...eries-in-series-and-parallel-at-the-same-time

Still wondering about them having to modify to fit Odyssey 6TL batteries though. That doesn't make much sense to me. If those do in fact require modification, does anyone know where to get new 6TL batteries that are drop in replacements?
 

NDT

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All military batteries with "6" in the nomenclature are the same size (6TL etc). If you desire AGM batteries, the military Hawkers are perfect, I'm running 8 of them currently using a BatteryMinder tender. Sure you can use only two batteries on the FMTV trucks, connecting them properly is child's play for anyone knowledgeable. Check the height of any battery you wish to use, any taller than the stock battery and the compartment lid may not fit.
 

SCSG-G4

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Civilian Group 31 batteries usually fit easily where 6TL's went (actually they are not as wide) and most deuce owners use that size when they replace their 6TL's. You can almost get three of them where the two 6TL's fit, prefect for a dual voltage application - 2 in series for 24 volts, and the third for 12 V applications.
 

DiverDarrell

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My truck is running great on 2 6tl’s. Also I call complete BS on having to adapt a battery tray for different brand 6tl’s. A specification for the 6tl is for the dimensions. You can get 6tl’s at Napa auto zone, interstate, and many other places.
 

porkysplace

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Kinda makes you wonder how much they will charge you for Blinker Fluid .

It sounds like they are trying to tack on a extra $500 or so to change the batteries, that most likely have to be removed during the RV build anyway.
 

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DiverDarrell

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Seems shady. I pulled 4 and have replaced 4 in about 40 min total. 20 to remove 20 to replace. This included getting my tractor out and installing the forks. I had to do this when I first got my truck to charge the batteries. The other day I found two of my batteries had gone bad. It took 40 min to pull two and re-configure the wiring to run off two batteries for 12 & 24. Would have been faster but I wanted to double check everything so I wouldn’t melt terminals.
 

Duckworthe

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San Diego, Ca
I replaced my batteries with the Odyssey batts in my truck. They fit into the tray but the lid wont just go back on because the batteries I had purchased also have screw terminals on them. They show that they can be removed but they wouldn't come off on mine and I didn't want to break them as they were just to dang tight. The center hold down needed to be modified because with the screw terminals and the regular posts, the wiring wont lay in the exact same locations and that also makes the center hold down not fit correctly. It took me about 2 hours to modify and get it all to work. The batteries are great and now sealed AGM so I have one less maintenance item to worry about. They are expensive! But mine are warrantied (in writing) for 8 years. That is a no questions asked warranty. If any one of them fail it is replaced on the spot at any location. Not just the Location that I bought them! Sorry I don't have pics right now.
 
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exon111

Member
35
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Location
OC, CA
I replaced my batteries with the Odyssey batts in my truck. They fit into the tray but the lid wont just go back on because the batteries I had purchased also have screw terminals on them. They show that they can be removed but they wouldn't come off on mine and I didn't want to break them as they were just to dang tight. The center hold down needed to be modified because with the screw terminals and the regular posts, the wiring wont lay in the exact same locations and that also makes the center hold down not fit correctly. It took me about 2 hours to modify and get it all to work. The batteries are great and now sealed AGM so I have one less maintenance item to worry about. They are expensive! But mine are warrantied (in writing) for 8 years. That is a no questions asked warranty. If any one of them fail it is replaced on the spot at any location. Not just the Location that I bought them! Sorry I don't have pics right now.

Ahhhh ok thank you. I was beginning to suspect this may be the issue after reading in a different thread that overhead clearance is tight in there and that these had an extra post. Makes sense now.
 

snowtrac nome

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I just replaced mine with 2 8-d batterys the tray does have to be modified and the 8-ds are a little wider. My cover wont fit down over they battery's right, I think a little heat in the box and I can get the wires to lay right, but at - 25 have fun trying to get those wires to flex. New batterys and 5w40 synthetic the truck had no problems starting today at -25.
 

juanprado

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You can also get 6tl at O'reilly's. My son works there and that is where I get them.

NAPA does also sell. Just a word of caution as in another lifetime I was a NAPA distribution warehouse manager, Check the date codes.... They don't sell many and they tend to sit a long time before being shipped to stores. Make sure you are getting a fresh & charged battery.
 

exon111

Member
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Location
OC, CA
I just replaced mine with 2 8-d batterys the tray does have to be modified and the 8-ds are a little wider. My cover wont fit down over they battery's right, I think a little heat in the box and I can get the wires to lay right, but at - 25 have fun trying to get those wires to flex. New batterys and 5w40 synthetic the truck had no problems starting today at -25.
How did you do this? You need both 24v and 12v right? I read you can't hook 2 batteries both in series and parallel. Are you using one 24v battery for the 24v side and one 12v battery for the 12v side of things?
 

Aernan

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San Jose/California
You can buy Hawker 6tl batteries directly from them. The oddesy is the retail brand and the batteries are different with that extra post. I bought 2 batteries from Napa. They are flooded cell and you must add acid. The hawker is an AGM which is better then flooded cell.

Sent from my SAMSUNG-SM-G930A using Tapatalk
 

snowtrac nome

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How did you do this? You need both 24v and 12v right? I read you can't hook 2 batteries both in series and parallel. Are you using one 24v battery for the 24v side and one 12v battery for the 12v side of things?
you don't have to you just hook in series, the 12 volt lead goes to the 12 v positive post, and 24 volt to the to the second battery. it really simplifies wiring. The only problem I have right now is clearance in the cover, I think I can resolved, once I get the wires warmed up and laid down right.
 

Aernan

Member
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Location
San Jose/California
that 8d battery looks 12V. To get 24V you will need two 12V batteries in series. So if you want to separate the 12/24 you would need. 2 batteries in series = 24V and one 12V battery or two 12V in parallel.
 

Storm 51

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I put two of the 6TL's in my little truck when I did the 100 Amp Generating System conversion and Battery Box modification contained in the Tech Bulletin.

It was a tight fit, but not some "impossible dream" installation.

If possible, you might just want to go have a look yourself to be sure you understand the issue and make sure someone isn't trying to "magnify a small problem into a large payday".
 

exon111

Member
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Location
OC, CA
We replace 6TL's with 8D's on all of our Acela Monterras...very nice upgrade...if ever an issue, 8D's are available anywhere. Is your build on an FMTV or an SD Brazos?
That's exactly why I wanted to do this swap. Do you do what the poster above described, basically hook up the two 12v in series to get 24 and just use the terminals on one of the batteries for 12v?

The truck in question is a SD Brazos with Cummins engine. Aside from that difference, it's mostly identical to the FMTV. Battery setup looks the same to me.
 
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