NEED dual batteries for fridge?

[rusty_tlc]

Datasheet for 34/78 Yellow Top:
http://www.optimabatteries.com/_media/documents/specs/D34_78_082104.pdf

Plugged in the numbers, left DoD at 100% and discharge at 2 A-hr.

n=1.04 (curious).
Cpeukert = 57.5 A-hr
T = 27.9 hours.

I have my doubts, so I tried with a Blue Top 34M.
http://www.optimabatteries.com/_media/documents/specs/34M_082304.pdf

n=1.08
Cpeukert = 53.8 A-hr
T = 25.4 hours

Not sure what to make of it all other than Optima's published numbers are goofy. According to this the Yellow is better by 2 hours or so, but the Blue is no better than the Red in capacity. I guess the difference will be that the Blue won't die with deep discharges like the Red, so a 100% DoD is real for it while 50% is all a Red Top can do. In fact, that must be it, so a Blue Top has in real life maybe around twice (or so) the capacity.

As I understand it there is a fundamental difference in the design of starting batteries and deep cycle batteries. It's been to many years for me to remember the specifics but IIRC starting batteries have a larger plate area which allows for fast discharge, deep cycle batteries have a smaller plate area which won't discharge as fast but thicker plates which will last through more charge/discharge cycles.

Or something like that.

Whatever the case, the two batteries are designed for two different applications. I'm sure a starting battery will survive many deep discharges, but not as many as a battery designed for that application. Conversely a deep cycle battery will work as a starting battery, but it will not last as long as a battery designed for that application.

It comes down to the right tool for the job.

Back to the OP's question.
Do you strictly need dual batteries with a fridge?
As usual the answers is, it depends.
If you do an occasional weekend trip probably not, as long as you have a back up plan to start your rig.
If you do a lot of trips and can live with a shortened battery life probably not<Insert back up plan caveat here>.
If you do a lot of trips and want optimum life out of your batteries you will want a dual battery set up with a deep cycle to run the fridge and any other accessories, like electric blanket or lap tops, and a second battery for starting and winching.

Winching?

A winch is a lot like a starter motor, it requires a lot of current in a short time, something deep cycle batteries don't do well. It would be a mistake to run it from a deep cycle battery.

Or I could be full of it. ;D

 

[Bogo]

Lots of good information in this thread. I'll add if you add solar, use a charge controller so you don't cook your batteries.

On Rusty's battery type explanation: Correct except when it comes to AGM batteries. AGM batteries can exhibit good deep discharge life expectancy and still have excellent starting capacity, but that again depends on design.

On Deka batteries. I'm a fan of them but that may be totally due to the fact they bought out the Voltmaster battery plant here in town. The Intimidator looks like what I'll be getting, but I'll be installing 4 group 31s. I have laptops and other electronics to run as well as refrigeration.

Another thing I'll add is if you can go 24V, do so. All the devices I've looked at are more efficient in 24VDC. Sometimes by as much as 10% more efficient. Usually it is from 4% to 8%. If you only have a 12VDC alternator you can get a 12VDC to 24VDC charge controller that will charge your batteries from the alternator. Personally I'd add a 24VDC alternator as a second alternator.

 

[Tucson T4R]

I opted for battteries out the ying yang. :sombrero: In my 4runner I run a dual Odyessey battery set up with a 1700 primary and a 925 secondary as a back up self jump starter when needed.

In my trailer I run dual Deka group 31 Intimidaters. Both set ups are working great. I did have the Odyssey 1700 fail after 4 months but that was replaced under warranty. No other problems with either set.

I go out frequently by myself in pretty remote areas that I would not want to walk back from, hence the battery over kill.

 

[cstamm81]

Tucon T4R, do you have a link to those Deka group 31's? Are they indeed deep cycles? I looked at their official site, but was unclear which of the Intimadators are actually deep cycle.

 

[Tucson T4R]

Tucon T4R, do you have a link to those Deka group 31's? Are they indeed deep cycles? I looked at their official site, but was unclear which of the Intimadators are actually deep cycle.

They are deep cycle AGM batteries and I liked that because I mounted them on their side. I purchased mine from the AT Trailer boys so I don't have a link to the actual Deka site. AT has had great experience with the reliability of these batteries so I took advantage of their experience and bought mine through them.

http://www.adventuretrailers.com/12volt_solar.html

 

[Bogo]

Tucon T4R, do you have a link to those Deka group 31's? Are they indeed deep cycles? I looked at their official site, but was unclear which of the Intimadators are actually deep cycle.

http://www.eastpenn-deka.com/assets/base/1143.pdf

Looks like they are a dual use deep cycle/starting battery. They will handle high current output as well as deep discharge. You may also want to look at the Sea Mate line. I've been trying to locate the PDF where they give the deep cycling life expectancies.

 

[highlandercj-7]

IMHO, it's easier to run Dual batteries than to try to find a place to store a jump pack. Most of them ore junk to boot, and the quality ones are huge. I'd run dual batteries and an isolator, that way you can run the fridge off one and if it goes dead your not stranded.

 

[TheRoadie]

I had the same problem with the housing of a jump box, so I just disassembled it. The 9 amp-hour battery was only about 2"X4"X6" and I hooked it up in parallel with my main battery with a cutoff switch for isolation. The charging circuit can be thrown away with the housing since you can just close the isolation switch and charge the jump battery in the vehicle. I can't carry this to another vehicle to help them out, but if they're within 20 feet I have cables. I don't have room for a full second battery under my hood, but everybody should be able to find a 2"X4"X6" volume.

That said, I still use a second deep cycle behind the driver's seat for the fridge.

 

[LandCruiserPhil]

I had the same problem with the housing of a jump box, so I just disassembled it. The 9 amp-hour battery was only about 2"X4"X6" and I hooked it up in parallel with my main battery with a cutoff switch for isolation. The charging circuit can be thrown away with the housing since you can just close the isolation switch and charge the jump battery in the vehicle. I can't carry this to another vehicle to help them out, but if they're within 20 feet I have cables. I don't have room for a full second battery under my hood, but everybody should be able to find a 2"X4"X6" volume.

That said, I still use a second deep cycle behind the driver's seat for the fridge.

Great solution to a back up starting battery.

Any pic available of your set up?