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Old 01-14-2007, 01:19 AM   #1
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Default Two 6 volt batteries or two 12 volt batteries

Which is better: two six volt batteries in series or two twelve volt batteries in parallel? I've seen this asked more than once.

Here's what I think:

Generally speaking, and for the "average" RVer, two deep cycle 6v golf cart batteries will outperform and outlast two "normal" RV 12v batteries.

IMO, two 12v should outperform two 6v if the amperage draw is really high such as for Microwave oven use through an inverter. 6v batteries have 3 x 2+v cells and 12v batteries have 6 x 2+v cells. 12 cells sharing a high current load will outlast 6 cells sharing the same high current load because the load on each cell is less. Peukert's Law states that as the rate of discharge increases a battery's capacity decreases. "Average" RVers don't run their microwave ovens off of their batteries so, at low current draws, Peukert's Law has much less effect.

6v deep cycle golf cart batteries are great for typical RV usage. They are too tall for the battery compartments on my RT

Quite often 66lb Trojan T105's 6v batteries are compared against 47lb Group 24's or 55lb Group 27's. Using that logic one could say that Trojan J150 12v batteries are better than the 6v Trojan T105's and be right but it is not a fair comparison. The Trojan J150 weighs 84lbs.....................

When it comes to batteries, the biggest and heaviest is often the best!
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Old 03-17-2013, 05:03 PM   #2
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Default Re: Two 6 volt batteries or two 12 volt batteries

I have to be honest with you. I don't understand the mechanics or operation of the 12V system in the RV at all. Sure I know that some of the equipment (lights, furnace fan, fantastic fan, radio/DVD player, water pump, LP gas detector, TV? ... etc) run off the 12 V system which in my case is run off of one 12 volt coach battery. I also know that there is a converter/inverter in the unit that converts 110 V AC power down to 12V DC so I can use my lights etc. while plugged into 110V shore power.

Does the TV and refrigerator ... when on 12V battery power actually run on 12V or is it being inverted (if that is the correct term) to 110V AC by the inverter??

PLEASE ANYONE STEP IN AND CORRECT ME AND OR/OR GUIDE ME THROUGH THIS!!!

Say for example ... if I disconnected the battery at the battery terminal ... would the 12 V systems still work if I was plugged into shore power (not that I would do this ... just want to get a better understanding of what is happening and why) I am presuming that the converter would kick in and convert the power from 110 AC down to 12 DC for the equipment needing 12V.

On the other hand ... if I was on battery power only ... I understand that the inverter takes that 12 V DC power and inverts? it up to 110V AC for those devices that require 110V. This is where my confusion really kicks in. To the best of my knowledge when I am on 12V power I am not aware of any devices I am using that use 110V. I don't use the microwave ... never tried unless plugged in. I know that I can't use the coach AC. I understand that some of the 110 outlets might be hooked into the system to run 110V appliances on 12V??? If so I don't think I have ever tried it. From what I've read doing this would be a huge drain on the battery(s)?

I do have a CPAP machine but I plug that into the 12V receptacle for power. Whenever I charge my batteries for phone/camera/computer ... again I plug into portable inverter that is plugged into the 12V receptacle.

I know that for those more expereince this may seen rather simplist and naive of me ... but hey ... it is what it is.

If there is another thread dealing with this topic please direct me to it ...

And finally ... why are two 6 VOLT golf cart style batteries better than 2 12 VOLT batteries. I'm guessing it's not about the total number of volts but the amount of amps that are produced??
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Old 03-17-2013, 09:08 PM   #3
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Default Re: Two 6 volt batteries or two 12 volt batteries

I have heard it said that two 6v batteries "usually specified golf cart batteries" will out last two 12v ones but no one ever pulled the specifications for equal comparison. I personally like the 12v ones if for any other reason if one goes bad you can disconnect the bad one and use the good one as is "to get you through" and you may have use for a battery for something else. You can't do that conviently with 6 v batteries. Keep in mind if you put in a new battery it is reccomended to change both, and with 6v that means changing both. If you have two 12v ones that is where you may use the other one someplace else. Guess what I used on my lawnmower for a couple years. A used 12v one from my snowplow truck when I had to change one I took the good one and put it there. It was better than buying a new mower battery. fortunatly it didn't take much for it to fit.
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Old 03-17-2013, 09:18 PM   #4
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Default Re: Two 6 volt batteries or two 12 volt batteries

Quote:
Originally Posted by g1g
I have heard it said that two 6v batteries "usually specified golf cart batteries" will out last two 12v ones but no one ever pulled the specifications for equal comparison. I personally like the 12v ones if for any other reason if one goes bad you can disconnect the bad one and use the good one as is "to get you through" and you may have use for a battery for something else. You can't do that conviently with 6 v batteries. Keep in mind if you put in a new battery it is reccomended to change both, and with 6v that means changing both. If you have two 12v ones that is where you may use the other one someplace else. Guess what I used on my lawnmower for a couple years. A used 12v one from my snowplow truck when I had to change one I took the good one and put it there. It was better than buying a new mower battery. fortunatly it didn't take much for it to fit.
Thanks "gig". I'll keep your thoughts on the matter in mind. I want to add a second coach battery sometime soon, if I can. Not sure whether there is enough room, although I understand that the 2013 ERAs have the option of having a second coach battery. Hopefully adding an extra one to the 2012 will be an easy task.
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Old 03-17-2013, 10:59 PM   #5
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Default Re: Two 6 volt batteries or two 12 volt batteries

I have read a couple of threads here about batteries and thought I would add a little insight. How you use and charge the coach batteries is very important in the type and volt of battery that will work best for you. Like Marko said 6 volt batteries are best for long lasting at lower amps, like boondocking for 4 days and running only lights and trying to conserve battery power. They work better and last longer when they are charged at a lower amp input. (10a to 15a) This is the normal charge when plugged into shore power. Most of the converters vary the amps of charge depending on the battery state. But, the rate of charge, or "charge profile" is usually set for 12v batteries with heavy output at first then it ramps down as the battery is charged. If you want to get the most out of 6v batteries you should get a "golf cart " charger. This holds true for mat or spiral batteries like the Optima ect. There performance is not so good if the charger has the wrong profile. Smart chargers and converters are not as smart as manufactures lead you to believe.

I use 2 31 series 12 volt batteries because it work for the way we use out B. We go for 1 or 2 night most weeks and usually dry camp ( mostly casino parking lots ) we also have used it all winter, running the furnace all night. In other words we use the batteries hard for shorter periods. We will drive for 2-4 hours and that is enough to charge the batteries. Which is another reason for the 12 volts. The alternator on the engine charges at much higher amps than 6 volt golf cart batteries like.

Fresh batteries are better than old. Spending $200 every 2 or 3 years on new 12 volt Interstate or equivalent batteries has worked better than trying to get 5 or 6 years out of batteries that cost 3 times as much.
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Old 03-17-2013, 11:20 PM   #6
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Default Re: Two 6 volt batteries or two 12 volt batteries

Hi "slipbobber" ...

Your use sounds very similar to mine. I can't say that I have ever had any concerns until this winter. The battery went "dead" for a short while even though the temperatures were warm ... so fortunately it didn't freeze. How did I know the battery was dead?? The LP gas detector light was red and sounding an alarm and the panel was showing RED for the battery level. I think I left a radio running. Anyway ... When I realized it I was on my way out so I just let the engine charge it and and never plugged in. When I went out later in the day ... I again relied on the engine to do the charging. As I was using batteries that evening I noticed my TV starting to flicker ... as if I was losing a TV signal. Seemed strange so I check everything including the battery level on the panel and it showed low. I was also running the furnace as well.

At that point I turned everything off and fired up the generator for a couple of hours. It seemed to charge the battery ... at least it showed FULL on the panel.

Now ... since then I haven't really had to use the RV although I have had it plugged into shore power to ensure it is totally charged. I'll get a chance to check it later this week when on a day trip.

If I find that I have any problems with it ...then it will be time for a new battery. At that time I will look at getting the extra one as well. This is all a learning process for me.

Thanks for your input ... much appreciated.
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Old 03-18-2013, 12:43 AM   #7
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Default Re: Two 6 volt batteries or two 12 volt batteries

12 volts comes from the batteries or the 110v to 12v converter.

110 volts comes from grid power, a generator or a 12v to 110v inverter.

Not all Class B vans come with an inverter.

TV's can be either 12v or 110v - depends on the TV.

It is not likely that a fridge will be run through an inverter in a Class B. I set mine up that way to run the fridge on 110v while driving the van. Running a fridge on 12 volt should be avoided unless the van motor is running or run on 12v only for short periods because it would draw down your batteries quickly.

There are exceptions to that - some vans will have 12v compressor fridges. Typically though, Class B's have ammonia absorption fridges. The ammonia needs heat from: 1. propane, 2. 110v electric element or 3. 12v electric element - in order to cool the fridge.

Quote:
Originally Posted by Karsty
Say for example ... if I disconnected the battery at the battery terminal ... would the 12 V systems still work if I was plugged into shore power (not that I would do this ... just want to get a better understanding of what is happening and why) I am presuming that the converter would kick in and convert the power from 110 AC down to 12 DC for the equipment needing 12V.
Yes - it can work like that. My converter can work without a battery and supply 12 volts. Some might not though so it is best to read the owner manual for the converter to know for sure.

Quote:
Originally Posted by Karsty
On the other hand ... if I was on battery power only ... I understand that the inverter takes that 12 V DC power and inverts? it up to 110V AC for those devices that require 110V. This is where my confusion really kicks in. To the best of my knowledge when I am on 12V power I am not aware of any devices I am using that use 110V. I don't use the microwave ... never tried unless plugged in. I know that I can't use the coach AC. I understand that some of the 110 outlets might be hooked into the system to run 110V appliances on 12V??? If so I don't think I have ever tried it. From what I've read doing this would be a huge drain on the battery(s)?
It depends whether or not your van has an inverter installed and also the capacity of the inverter and how it was installed (adequate sized wiring).

Often the inverter (if there is one) is small and only meant to power the TV and DVD and maybe charge your phone etc.

Typically it is an aftermarket inverter installation if the inverter is sufficient to run the microwave oven. Some very new Class B's have this capability.

Quote:
Originally Posted by Karsty
And finally ... why are two 6 VOLT golf cart style batteries better than 2 12 VOLT batteries. I'm guessing it's not about the total number of volts but the amount of amps that are produced??
Yes, it is all about the amp hour capacity. 6 volt batteries tend to be larger and heavier and they are true deep cycle batteries meant for mobile use - bouncing along in a powered golf cart. Basically, bigger heavier batteries have more capacity. 2 batteries are better than one for sure
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Old 03-18-2013, 12:59 AM   #8
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Default Re: Two 6 volt batteries or two 12 volt batteries

markopolo ... Thanks for taking the time to enlighten me. Much appreciated. The only time I run 12V on the fridge is when I have the engine running. Mine is a three way fridge and I have it set to "AUTO" and it selects the source that is best. Whenever I boondock I use propane ... and of course if I am plugged in 110 V.

Darn ... one of these days I will have to pull out the manuals and see what is what.

Thanks again.
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Old 03-22-2013, 11:43 PM   #9
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Default Re: Two 6 volt batteries or two 12 volt batteries

Quote:
Originally Posted by g1g
I have heard it said that two 6v batteries "usually specified golf cart batteries" will out last two 12v ones but no one ever pulled the specifications for equal comparison. I personally like the 12v ones if for any other reason if one goes bad you can disconnect the bad one and use the good one as is "to get you through" and you may have use for a battery for something else. You can't do that conviently with 6 v batteries. Keep in mind if you put in a new battery it is reccomended to change both, and with 6v that means changing both. If you have two 12v ones that is where you may use the other one someplace else. Guess what I used on my lawnmower for a couple years. A used 12v one from my snowplow truck when I had to change one I took the good one and put it there. It was better than buying a new mower battery. fortunatly it didn't take much for it to fit.
I think the redundancy of 2 X 12V batteries is a good reason to go that route. As you say, if one battery goes bad (dead cell), you can still draw 12V from the surviving twin. I'm not sure that would be possible with 2 X 6V connected in series, but I could be mistaken. If a cell goes dead in series, there's either very poor or no connectivity, I think.

Here's an interesting weblog I stumbled across while researching the failed cell issue in a series installation. Long, but a good read.
http://www.wagonmaker.com/newbatt.html
Some more webpages about battery system configuration differences with healthy banks and banks with fault conditions.
http://batteryuniversity.com/learn/arti ... igurations
http://www.chromolywally.com/?p=219
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Old 03-23-2013, 01:20 AM   #10
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Default Re: Two 6 volt batteries or two 12 volt batteries

" ... if one battery goes bad (dead cell), you can still draw 12V from the surviving twin. I'm not sure that would be possible with 2 X 6V connected in series, but I could be mistaken ... "

Mike, you make no mistakes. If one 6V in a series is dead, all you got an expensive and corrosive paperweight.

Two 6Vs connected in series give 12V (in series, voltages add). Both batteries supply the same current, so both discharge at the same rate. Two 12Vs must be connected in parallel - but there is some chance that one will discharge faster than the other.

Battery life is usually the key issue and this seems to be where the series 6V configuration wins: this article on the battery life differences.
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