2- 6 volt batteries or large 12 volt battery

roamingaz

Explorer
I read through a lot of threads here but still not getting my questions answered.
My goal is to avoid the electrical disaster I had at overland expo when my 2 new optimas crapped out on me leaving me with no auxillery power to run a fridge, etc.
Most of my trips will be 2-3 days with one or two 7 day trips during the year, I need to be able to maintain a charge on a battery running a new model ARB fridge, small power inverter and a couple LED lights.
I was originaly going to get a Diehard platinum marine 12 volt but after doing some searching I found the 4D and 8D 12 volt batteries have twice the Amp hour rating and cost twice as much, 2 6 volt batteries would be 4 times the amp hours!
SO would I be better off with 2 6 volt batteries or stay with the single 12 volt?
Am I corect in my understanding that a 6 volt battery with a 220 amp hour rating would be 440 amp hours when adding another battery to get 12 volts?
That would be a huge amount of power reserve and would easily run my fridge for a couple days....right?

I want to keep my system simple and will charge/maintain with a 80 watt solar panel.

any suggestions would be awsome
 

kjp1969

Explorer
Our non-expo RV travel trailer uses two 6v golf cart batteries in series, and provides a massive amount of reserve power. We have numerous incandescent light, fridge, water pump and forced air furnace that stays at 66 all night, and we can still dry camp for 4-5 days.

I can't comment on durability of those batteries because ours is a smooth-roads RV, not an off-road machine. As for longevity, we replace them every 3 years or so, but just as a precaution. The 6v's are $60 or so at Costco. They are huge and heavy, too.
 

wrcsixeight

Adventurer
Two 6 volts batteries rated at 220 a/h each yield 220 amp hours when wired in series for 12 volts, not 440.

6 volt golf cart batteries are good because they are true deep cycle batteries. They have more room under the plates so more debris can accumulate underneath before a cell shorts out rendering the battery useless. They are a good deal because of the quantity made for golf courses. They are a couple inches taller. They say if you need to power high draw devices like a microwave then 12 volt batteries will suffer less voltage drop than 6 volt batteries, but unless you plan on drawing 150 amps for 10 minutes, this is not really a factor. If you can fit them in your proposed location, they will work much better than the Optimas. For their footprint, Optimas have poor capacity, which you found out the hard way.

It's about amp hours, not cranking amps unless you are starting an engine.

A lot of 12 volt batteries will claim "deep cycle" in their attributes. Most are not deep cycles but dual purpose battery, which is just a starting battery that is slightly more tolerant of deeper discharges. Most true deep cycle batteries will not list a cold cranking amps number, because they were not built/ designed to start an engine, but power a lower load over a longer time. Thus amp hours and reserve capacity are much more relevant figures for that purpose.
 

CanuckMariner/Nomad

Love having fun 😊 in the 🌞 by the ⛵ and the ⏳
Jess, I would be interested in knowing more about the 2 Optimas that crapped out on you. What age, both the same type, are they deep cycle, etc. Unusual to see two crap out unless something was left on for a long time and drew them down a bunch or hooked up wrong. What was hooked up to them and how, etc.

If they were true deep cycle (Yellow or Blue) then they should recharge up to normal over night or two. If they are less than a couple of volts to 6 V then you might have to charge first with a old manual charger before a newer smart charger will begin its cycle.

I have had mine for 5 years (Blue tops grp 31) with nary a problem. If they are new, they are still under warranty, get 'em load checked at an Interstate or Optima dealer.:costumed-smiley-007
 
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LandCruiserPhil

Expedition Leader
How do you go about installing lead acid golf cart batteries and give them proper ventilation while keeping them cool when mounted inside the cabin or camper?

roamingaz lives in Arizona where free air cab temps of 140° is not uncommon.
 

LandCruiserPhil

Expedition Leader
Jess, I would be interested in knowing more about the 2 Optimas that crapped out on you. What age, both the same type, are they deep cycle, etc. Unusual to see two crap out unless something was left on for a long time and drew them down a bunch. What was hooked up to them and how, etc.

If they were true deep cycle (Yellow or Blue) then they should recharge up to normal over night or two. If they are less than a couple of volts to 6 V then you might have to charge first with a old manual charger before a newer smart charger will begin its cycle.

I have had mine for 5 years (Blue tops grp 31) with nary a problem. Perhaps they are still under warranty, get 'em load checked at an Interstate or Optima dealer.:costumed-smiley-007

There is a good thread on the MUD board where "Optima Jim" talks about when folks think yellow Optimas are dead and just need the proper charging sequence to restore them. Not sure if that was Jess problem but worth a read if you use yellow Optimas.
 

cnynrat

Expedition Leader
I've been down this thought process a couple times, once with my Bigfoot camper, and again recently when one of the group 31's in my AT Horizon died.

Let's start with what I think you should not do, which is run two 12v batteries in parallel. Not sure, but this may have been what bit you with your Optimas. When running dual 12v in parallel, you think you might get double the capacity because in theory each battery will supply 1/2 the current. In reality small differences in the electrical characteristics of the batteries lead to them not sharing the load equally, which means one battery will discharge more rapidly. Another issue is parasitic discharge, which is when one battery charges the other because they aren't in an equal state of charge. Think about it, and you realize these two phenomena are closely related. So in the end, doubling the capacity proves elusive, and IMO these problems also tend to shorten the life of the battery.

You already got the answer to your question about whether you double the capacity running two 6v batteries in series. The reason you don't double the capacity is because both batteries are supplying the full current to the load. Say you have a 25 amp draw, well then both 6v batteries are supplying 25a to the load.

There are a couple other things to look out for with 6v batteries. One is that they tend to be tall, so you may not have room for them. For a while I wanted to go this way for my camper, but there was no way I was going to fit two 6v batteries in the space I had. The second issue is the charging voltage is often pretty high. Looking at the spec for a 6v Lifeline AGM battery, the voltage for bulk/acceptance/absorption charge is 7.1-7.3v That would mean to put both batteries in the most rapid charging mode you would need to provide 14.2-14.6v. My FJC voltage regulator tends to run between 13.2-13.8v. It would charge the dual 6v batteries at that voltage, but only at a slower rate. If you are talking about a trailer you also need to factor in the voltage drop in the wiring to the trailer, which will probably reduce that charging voltage even further.

So that brings me to what I think is the ideal solution, which is a single 12v battery appropriately sized for your requirements. In both my camper and the AT Horizon I've gone to a single group 4D battery with a little over 200 AH capacity. Expensive, of course, but not that much more than the cost of two group 31s with 90-100 AH capacity. Heavy, you bet, but actually marginally lighter than the 2 group 31s it replaced.

Hope this helps.
 
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CanuckMariner/Nomad

Love having fun 😊 in the 🌞 by the ⛵ and the ⏳
There is a good thread on the MUD board where "Optima Jim" talks about when folks think yellow Optimas are dead and just need the proper charging sequence to restore them. Not sure if that was Jess problem but worth a read if you use yellow Optimas.

For any noobs, that is www.IH8MUD.com

Exactly Phil. When I buy a true AGM deep cycle battery, I discharge them to zero volts (hook it up and leave your headlights on over night). Then charge with an old direct slow (2AMP) charger and once at around 6 volts, then switch to a smart trickle charger which goes though all the cycles. End result is a great battery that hasn't lost its capacity. Straight from Interstate and Optima, who both recommend this for new batteries. And also do this once every year or so to keep them conditioned. The new smart chargers have cycles in the to lessen or prevent sulphonation, hysteresis, and other common battery problems. Starting batteries do not like to be totally discharged.:costumed-smiley-007
 

wrcsixeight

Adventurer
I don't think his Optima batteries are toasted, just that they did not have enough capacity to meet his needs.

I don't know where he plans on possibly mounting the 6 colt golf cart batteries. I know they make sealed and vented battery boxes, but cannot find the 6 volt ones.

They do make sealed AGM 6 volt batteries too.
http://www.lifelinebatteries.com/rvflyer.php?id=14
 

wrcsixeight

Adventurer
For any noobs, that is www.IH8MUD.com

Exactly Phil. When I buy a true AGM deep cycle battery, I discharge them to zero volts (hook it up and leave your headlights on over night). Then charge with an old direct slow (2AMP) charger and once at around 6 volts, then switch to a smart trickle charger which goes though all the cycles. End result is a great battery that hasn't lost its capacity. Straight from Interstate and Optima, who both recommend this for new batteries. And also do this once every year or so to keep them conditioned. The new smart chargers have cycles in the to lessen or prevent sulphonation, hysteresis, and other common battery problems. Starting batteries do not like to be totally discharged.:costumed-smiley-007


I have heard of this being applied to NiCad batteries, but I have never ever heard of this being applicable to lead acid batteries. It goes against every thing I have ever real about the care and charging of lead acid batteries, and I would be very interested to read it from Optima or Interstate if you can provide a link.
 

roamingaz

Explorer
Alot of good infomation!
The Opitmas I had were yellow top 48 amp hour rated, they were both bought at Desert Rat in Tempe and less then a year old when they died. I am sure I had a lot of things contributing to there demise, I was using a old Norcold 12 volt fridge that sucked alot of power as well as regular 12 volt RV lighting, charging was done by a older 80 watt solar panel that was not the best quality. The first day at the Expo it was hot and the fridge was running constantly then the first night I had a bunch of lights on and by morning the fridge had shut off and the batteries were at 8 volts! my solar panel couldn't charge them enough except to run 1 light very dimmly. After I got home I did a slow 2 amp charge on them and they did charge back up but once I turned the fridge on they wouldn't hold a charge or run the fridge very well. I have since sold that camper and now I am starting fresh and want to do it right this time, I have a full size chevy and have plenty of room for whatever I need so now that I better understand the 6 volt batteries I think I would be better with a larger 12 volt such as the 4D to keep things simple.
I am also going to hook up a battery isolator so while I'm driving the altenator will help charge them back up and the solar panel will be for when I am parked.
 

LandCruiserPhil

Expedition Leader
I have heard of this being applied to NiCad batteries, but I have never ever heard of this being applicable to lead acid batteries. It goes against every thing I have ever real about the care and charging of lead acid batteries, and I would be very interested to read it from Optima or Interstate if you can provide a link.

I think THIS is the thread Optima Jim who works for Optima provides a lot of Optima info.
 

wrcsixeight

Adventurer
Nowhere does Optima Jim say it is good to drain the battery to 0 volts. His info says to keep the battery at or above 12.4 volts. His links to U tube videos show how to get a deeply discharged battery to accept a charge with a modern charger, by paralleling it with a good fully charged battery.

Lead acid batteries do not have a memory. They should never be discharged below 10.5 volts.

Draining a new deep cycle lead acid AGM battery to 0 volts intentionally and then recharging it fully to make it last longer is pretty much the most ridiculous statement I have read on any forum, and I hope it was typed tongue in cheek.

And Interstate does not make batteries. They market batteries. Johnson controls make their starting batteries, and US battery makes their deep cycle batteries.
 
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CanuckMariner/Nomad

Love having fun 😊 in the 🌞 by the ⛵ and the ⏳
Nowhere does Optima Jim say it is good to drain the battery to 0 volts. No one said he did. His info says to keep the battery at or above 12.4 volts. His links to U tube videos show how to get a deeply discharged battery to accept a charge with a modern charger, by paralleling it with a good fully charged battery.

Lead acid batteries do not have a memory. They should never be discharged below 10.5 volts.

Draining a new deep cycle lead acid AGM battery to 0 volts intentionally and then recharging it fully to make it last longer is pretty much the most ridiculous statement I have read on any forum, and I hope it was typed tongue in cheek, otherwise it is a sign of monumental ignorance. Quite the comments for a friendly discussion?

And Interstate does not make batteries. They market batteries. Johnson controls make their starting batteries, and US battery makes their deep cycle batteries.

Way too hostile to continue this discussion. You are taking this WAY too personal. Cool off and then comeback and edit your post accordingly. Seems a few threads on this forum are getting this way. I thought it was supposed to be a friendly exchange of ideas and experiences, not this!:costumed-smiley-007
 
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LandCruiserPhil

Expedition Leader
CanuckMariner Im also curious about bringing a battery to zero and back up. What is your source/link on this system? Also goes against everything I have read on batteries.
 

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