Six Or 12 Volt Batteries?

[maxrjs]

Are two six volt batteries better than one 12 volt battery? Or, given weight and space considerations, would it be better to go with two 12 volt batteries? We rented a trailer from our local dealer and he had two six volt batteries with a three amp solar panel. He said a six volt would give 40% more power than a 12 volt. We are buying a new 5-th wheel and I was thinking of trading the standard 12 volt towards two six volt batteries ... don't know if the dealer would even want to do that. Just wondered if six volt is the way to go ...

[JRTJH]

There was a recent poll on this forum about how people camped. The results were:

44 members (60%) - Always use hookups - Never Dry Camp
20 members (27%) - Mostly use hookups - Dry Camp sometimes
8 members (11%) - Half and Half - hookups & dry camping
1 member (1%) - Mostly dry camps - uses hookups sometimes
1 member (1%) - Always dry camps - never uses hookups.


So, why include this in a question about which battery is best?

If you're in the 87% of campers who always or mostly use hookups, a 12V battery for the occasional dry overnight will usually work well without the additional expense of 6V batteries and the modifications to house them, extra weight and unique battery boxes for the larger size battery.

But, if you're in the 13% that dry camp half the time or more, then double 12V batteries or better yet, 2 or more 6V batteries would provide more electrical capacity to make extended dry camping stays easier.

Either way, pretty much it's a choice you need to make based on financial considerations, convenience, generator (recharging) capability and personal preference.

For the largest storage capacity 6V is the way to go, but it comes with a price that you may not be able to justify unless you really need and would use the extra capacity.

[maxrjs]

Thanks! It looks like we fit into the 13% - desert campers. I had not thought of more than two 6v. We have a generator - one of those big ones that will run the AC - very loud! I have seen people use two small Hondas with a relay of some type to make them work together. Must be quieter and also can run the AC. I will try and search that out and if no answer then post a question: "What is the best protable generator option?"

[JRTJH]

HEHE If you post that question, you'll get the same type response as you'd get by asking which is better, Dodge, GM or Ford.... :bdance:

Sams Club is liquidating their champion 2KW inverter generators around this area. They are about the same noise level and electrical output as Honda, have a pretty good reputation and about half the price normally, on clearance for $299 around here which makes them 1/3 the honda price. Champion seems to have a pretty good reputation so that's a consideration if you're looking to upgrade to smaller generators that can be used in tandem to power a bigger load. They do the same thing Honda does with piggybacking.

[Festus2]

You can search the forum for portable generators or generators and you will find numerous posts about this topic, which by the way, has been discussed thoroughly. Various brands and models - including Honda and Champion - should appear so you should be able to get a good idea of what is out there with comments about each.

[SteveC7010]

I have a friend who outfitted his trailer with four 6vdc golf car batteries. He also installed about 300 watts of solar panels on the roof of the trailer. Check out his systems and mods at http://www.everymilesamemory.com/

[smiller]

To answer the original question, there is no inherent superiority in two six volt batteries in series over a '12 volt' battery as all lead acid batteries are a combination of multiple 2.1 volt cells in series. However, the 6-volt batteries commonly referred to for RV use (aka 'golf cart' batteries) are of a heavy-duty deep-cycle design that is lacking in many 12-volt alternatives, thus two 6-volt batteries of that type might well be a better choice than a lesser 12-volt battery. But the advantage is due to the difference in construction of the batteries themselves, not their design voltage.

[Festus2]

I was always understood that 2 - 6v batteries designed for RV and/or marine use, delivered more amp hours compared to similar 2 -12v batteries which would make them more suitable for dry camping. They both deliver 12v (if wired properly) and, in that sense, there is no difference. As you pointed out, there are also design and construction advantages of having golf cart-type batteries over the 12 v ones.
I agree with JRTJH's point that if you are going to be hooked up most or all of the time, it doesn't make a lot of sense to spend the extra $$$ to purchase 6v batteries.

[smiller]

I was always understood that 2 - 6v batteries designed for marine and/or marine use, delivered more amp hours compared to similar 2 -12v batteries which would make them more suitable for dry camping. Two (say) 100 amp-hour six-volt batteries in series will not deliver any more power than a 100 amp-hour 12-volt battery. That is to say, there is no advantage in the mere fact that there are two 6-volt batteries instead of one 12-volt because again, they are all really just cells in series. The advantage sometimes seen is because the 6-volt batteries often used in this application are of a heavy-duty nature, more so than the usual 12-volt alternatives. So the difference is related to the construction of the batteries (and the fact that they are not really equivalent), not 6x2 or 12x1.

[ktmracer]

talked to a trojan battery engineer at a local RV show about this exact topic. His comments were:

If you don't typicall draw heavy currents (<50A per 12V bank) , want to draw batteries down to 20-30% SOC (70-80% discharged), and dry camp a lot then golf carts are the way to go. Will offer the longest cycle life as long as you keep them watered. He said lack of water is the biggest cause of failure. Don't worry about drawing them down to 30% SOC repeatedly, they will take it for 100's of cycles, just watch and make sure you don't go below 20% SOC (discharge 80%).

If you want to consistently draw heavy currents (75+A per 12V bank) such as heavy inverter loads, and don't discharge as deep then 12V true deep discharge are the way to go since the 12V have much lower internal resistance. But they won't take as many deep discharge cycles, and should be kept above 50% SOC.

If you seldom dry camp, then just get a generic 12V RV/marine battery.

He mentioned many big coaches are going to 12V banks because of high current draw. Also, interestingly he mentioned folks that want a "hot" golf cart, stuff in the 12V banks for quicker acceleration (lower internal resistance hence higher max current). Those that want longer distances or longer battery life stick with 6V golf carts.

Also as a side note AH is dependent on discharge rate. Look carefully at a mfg AH ratings and compare the 20Hr rate to higher discharge rates. typically a golf cart 6V AH doesn't drop as much as a 12V does as the discharge rate increases. For example if the 20Hr rate is 100AH (5A), don't expect anything near 100AH at a 25A discharge rate, you won't get 4 hours it will be less. The 6V golf cart won't drop as much as a 12V but it will drop.

[JRTJH]

Most automotiive batteries have thin plates and relatively wide gaps between the plates. This allow them to discharge rapidly and to supply a large amperage for a short time. They are designed to discharge PARTIALLY and to be recharged before complete discharge (intermittent use) Their purpose is to provide large energy bursts needed to start cars/trucks, etc.

Most Deep cycle batteries have thicker plates and the plates are closer together. This allow them to have more plates in a specific sized area and to provide sustained discharge over a longer period of time and to discharge more completely before needing recharge. The plates, because they are thicker, don't warp as easily and will stand up to the heat/collection/discharge of electrons with more durability. Their purpose is to provide lower level energy for sustained periods of time. (Still, it is not recommended to discharge deep cycle batteries beyond 40-60%)

12 volt deep cycle batteries have 6 cells in a 6x7x11" (approximate) container. so each individual cell is about 6x7x0.8" 6 volt deep cycle batteries have 3 cells in about the same size container (or even larger). so each individual cell is about 6x7x1.8" (nearly 2 times thicker). That means the cells in 6 volt batteries are significantly larger, usually capable of storing more energy than a smaller cell size found in 12 volt batteries. Since the 6 V battery is designed to deliver low level energy for a long time, the plates can be closer together and still dissipate the heat generated by converting potential energy into electricity within the cells. ie: the ability to cool the battery is not as critical as in the automotive battery.

Sort of like a D cell battery will provide more energy than a AAA cell battery will provide, but both are 1.5 volts. The larger size cell allows for increased storage capacity.

There are other significant differences such as heat dissipation, recharge capability, plate construction, durability, etc, but essentially, 6 volt batteries have larger cells and can provide more energy per cell than most 12 volt batteries. HOWEVER, if an "ideal situation" where the 12 volt battery were exactly double the size of the 2 individual 6 volt batteries, so that the individual cells within the batteries were all the same size, the energy capability would be essentially the same between the 12 V setup and the 6 V setup. BUT: In that "ideal situation" The 12V battery would be able to provide a higher burst of energy than the 2 6 V batteries could provide (as was just described in the previous post) mainly because of the difference in plate thickness between the two differnet construction techniques.

[jje1960]

Nothing highly "technical" on my post..... Just that why do Golf carts use 6V instead of 12V batteries? Think this indicates something.

[ktmracer]

Nothing highly "technical" on my post..... Just that why do Golf carts use 6V instead of 12V batteries? Think this indicates something.

see my previous post on comments from a trojan engineer on choosing a rv battery (page 1).

from his explaination "golf cart" batteries were designed for use at moderate currents (75A or so max) with high cycle life and being able to be deeply discharged repeatedly (up to 80%DOD) and charged at a high rate without damage. By the way they are also used in industrial applications in fork lifts and lift trucks etc., charged and discharged heavily on a daily basis. I'm sure they demanded something that would last a long time while being abused constantly. It would be a rare RV'r that would ever cycle a set of golf carts as many times as the trojans are rated for. IIRC the life rating is in excess of 500 cycles to a 70% DOD (30%SOC) that's going to take lots of days camping!! In fact it take something like 50 charge discharge cycles at 50% DOD before trojan golf carts hit their maximum AH capacity per info on the website. Course you pay for this capability as well, last I checked a pair of trojan golf carts were 3-5x more expensive than a pair of off the shelf 12V RV/marine batteries.

Now remember electric golf carts/fork lifts etc. have been around for many decades so I suspect there is some legacy and resistance to switching as well. Lots of battery improvements have occured in the last 50 years or so, and electric golf carts/fork lifts have been around at least that long.

12V deep discharge only have made signifcant strides in the above areas as well since the 60's. And not all golf carts have 6V some people swap out for 12V if the want a "hot rod" golf cart with faster acceleration. 12V will give higher peak current by their design, but sacrifice cycle life and can't take as deep a discharge.

It's differences in the basic construction (plate material, thickness, other metals added to the lead, etc.) not basic chemistry that results in the performance differences and what the battery is optimized for. They are all lead acid, and have the same volts/cell and pretty much the same watts/lb that derive from the basic chemistry. Fundamentally a 12V could be made to perform like a golf cart, and a 6V could be made to perform like a 12V starting battery. Go back to the 1950's and almost all cars had 6V batteries, not 12V.

And as mentioned on the previous page and a response above, if you typically run heavy inverter loads, golf carts probably aren't the best choice, then a good 12V deep discharge is probably a better choice. And if you seldom dry camp for any length of time, golf carts are probably an overkill, expecially given the expense.

Personally I run the golf carts since I don't have heavy draws (typically less than 30A, but occasionally 50-75A for a few minutes) , discharge the heck out of the batteries (often down to 20%) charge them at C/3 rate (90+A) and I can't kill them. One set is going on 8 years, probably 20-30 charge discharge cycles/year. Second set is only a year old, but the same kind of "abuse". Kinda like what a real "golf cart" sees!

[smiller]

The ability of a lead-acid battery to withstand deep cycling or provide high current or have a low internal resistance has primarily to do with thickness and composition of the plates and electrolyte chemistry has nothing to do with whether the battery happens to be 6 or 12 volts. Usually the '6 to 12 volt' comparison threads involve comparing apples and oranges (as this one is), and that is the result of the differences noted, not voltage. OK, I've said it every way I can now. :D

[mhs4771]

If you want Batteries, go get two 12V 8D batteries, be carefull they're 150 Lbs each, but you'll have plenty of battery power.

[suza]

I have a friend who outfitted his trailer with four 6vdc golf car batteries. He also installed about 300 watts of solar panels on the roof of the trailer. Check out his systems and mods at http://www.everymilesamemory.com/

Thanks for the link to the boondock blog. Lots of great mods and tips for dry camping.

[Andymon]

I have a friend who outfitted his trailer with four 6vdc golf car batteries. He also installed about 300 watts of solar panels on the roof of the trailer. Check out his systems and mods at http://www.everymilesamemory.com/

Great link!! Thanks for posting that!!

[mwhit]

Since I got a new camper with a new 12V battery, I opted to add a 2nd 12V battery.
I installed a 1-2 battery switch and set on ALL when connected to shore power. When we dry camp I switch to use only #1 battery to run the camper 12V items. Battery #2 is connected to a 1000 watt inverter that is used to power my LED TV and satellite receiver. The next day when the generator can be used I switch to ALL and charge both batteries. I have installed volt meters to monitor each battery. My 12V batteries are both Interstate deep cell batteries.
https://www.dropbox.com/s/clayx24guh00zfv/2013-07-21%2020.12.59.jpg
Hope this may help someone. Mike

[suza]

Since I got a new camper with a new 12V battery, I opted to add a 2nd 12V battery.
I installed a 1-2 battery switch and set on ALL when connected to shore power. When we dry camp I switch to use only #1 battery to run the camper 12V items. Battery #2 is connected to a 1000 watt inverter that is used to power my LED TV and satellite receiver. The next day when the generator can be used I switch to ALL and charge both batteries. I have installed volt meters to monitor each battery. My 12V batteries are both Interstate deep cell batteries.
https://www.dropbox.com/s/clayx24guh00zfv/2013-07-21%2020.12.59.jpg
Hope this may help someone. Mike

Thanks, Mike. I'm beginning to understand the solutions people are using to keep things running on battery :) What are the digital readouts?

[mwhit]

The digital readouts are the voltage meters displaying the battery voltage of each deep cycle battery. My both batteries sit side by side in the tongue rack. My RV had a Onan generator installed but removed because I have 2 Honda EU2000i. I was able to use the battery cables that connected the generator for my 2nd battery to power the inverter.

[suza]

The digital readouts are the voltage meters displaying the battery voltage of each deep cycle battery. My both batteries sit side by side in the tongue rack. My RV had a Onan generator installed but removed because I have 2 Honda EU2000i. I was able to use the battery cables that connected the generator for my 2nd battery to power the inverter.

And, I'm sure more reliable than the battery indicator on the control panel :) Would a two 6V Golf Cart configuration need two or one voltage meters? Does the meter/display use much power, or can it be easily disconnected to save batteries?