12 vs 6 volt batteries

[Wolfgang92025]

OK,

Need some help.

On one of the recent batteries subject the discussion was around 2 batteries and problems with keeping both batteries healthy.
If I remember right, 12 volt parallel circuit it is difficult to keep batteries in good health ???

So, below are my two options.
Both set-up's will give me 12 volt nominal.
Ignoring battery cost, weight, etc., which one is the better choice? and why




Thanks in advance for your help in understanding.

Wolfgang

[jeep_bluetj]

You'll get a few different answers on this.

For oldskool flooded batteries:

If the 2 12's are the same brand/type battery, the same age, the drain factors from being in paralell are very minor. This is more true if you keep a good charger and/or a load on it. The only time matched batteries discharge each other to any sigificant amount is storage. IOW, there have been lots and lots of RV's with 2 12's in parallel and it works just fine. Mismatched batteries don't fare so well in this application.

BUT, even tho all that's true, I vote for 2 6's. Why?

1. A golf cart battery is designed with big plates, lots of lead, and is generally quite rugged.

2. You can pick 'em up at Costco/Sams pretty cheap.

3. They really are deeeeeeep cycle. WallyWorld marine batts aren't.

Other battery types (AGM/sealed/etc..) are slightly different. But bang-for-buck I'll stick with 2 golfcarts If I need lots of juice.

But that's only if you need 200+AH. That weighs alot. For the tent trailer, I used one deep-cycle optima. Smallest one made (20aH or so? I can't remember.) It was rugged for off-road, could be mounted on it's side, had enough power for the ligthts, and weighed in less than 20 lbs. In contrast, the 2 6V golf cart batteries in my motorhome weigh well over 100lbs for the pair. (And I need to water them, etc....)

[wannabefree]

Yep, all that.

Parelleling batteries is generally not good, though often done. The reason is that even two identical batteries are never identical. One will fail before the other, and when that happens you shorten the life of both as the "good" one discharges into the "bad" one, turning energy into heat, and speeding global warming

OK, your contribution to global warming will be relatively small if you parallel batteries but your batteries, both of them, will fail faster. There are sophisticated battery management thingies that can prevent the problems of paralleling, but they are pricey, which is why the cowboys (no offense cowboys -- maybe trailer jocks is a better term) just tie a bunch of batteries in parallel.

Me -- I use a 35Ah gel cell. It runs my fan and lights about 4 days without a charge (not all the time, of course), which is plenty.

[wlooper89]

My battery is a 110 AH AGM RV battery. I would look at something else now, having learned a little more about batteries. Mine has a somewhat high cranking amp rating which is generally not good for deep cycle capability. Engine start batteries have lead plates with a sponge shape to give a lot of surface area for high cranking amps. The problem is that the sponge shaped plates tend to crumble under repeated deep cycle and end up in the bottom of the battery case. A battery that is not intended to start an engine, as with golf cart, boat trolling motor or solar power system, is more likely to have solid flat lead plates with better deep cycle capability.

Deep cycle batterys tend to be heavier because of the thicker and more solid lead plates. That is definitely a consideration for me, especially since my back surgery. My 110 AH battery weighs 78 lbs. Two batteries that each weigh less would be a plus for me.

AGM material between the plates if possible is still my choice because, like gel cell, the battery can be sealed and AGM is less sensitive to higher voltage charging, to which the tow vehicle or some chargers might subject the battery. But cost is also a factor and the flooded cell batteries certainly have the advantage in that regard.

I would not worry too much about using two batteries if they are identical and start out new together. This may be the best option if you want a lot of AH's, and want to be able to lift the batteries without too much strain. When the time comes I would replace them as a pair like the D-Cell batteries in a flashlight.

Keeping batteries on a maintenance charge when not in use is also good. I cannot do that when my trailer is at its storage place, so I try to bring it over to the house once a month in the off season to charge it up again. Usually I am working on the trailer anyway and have it in the garage for that.

Bill

[jeep_bluetj]

Whee... I'll post more... (As I've been working on a battery charger project, so batteries are on my minde lately...)

The OP really asked "what's better, 2 12's or 2 6's, but not in terms of cost and weight.."

Problem is, cost/weight/power/battery type are FAR more important than if it's a paralell or series configuration. That's really the last determination, there's so many well-functioning parallel battery examples out there that it's a no-op to me. Determine how much power you need, determine how much space/weight you can afford, buy the best price point battery/set of batteries that gives you that. If you'll the type to NEVER check the water in the battery, don't get a flooded battery - you need a SLA or a AGM (which may/may not determine if you pair as 12v or 6v or a single battery)

So if I need around 200ah, and I want it to last 3-5 years or so, and I got space for T105 GC batteries, 2 6v GC batteries are the way to go. If I've got space for 1 Group 51 battery, there's no way to do it (reasonably) with 2 6v batts. Better off with 1 D51. (And I doubt there's any way to get 200AH into that space, maybe not even with li-ion, which would cost a bundle)

And if I'm looking at needing 400aH or so, I may end up with 4 T105's in series-paralell ($300). To get 400ah with just 2 batteries ends up being more than $500. (But they're better batteries too)

[wlooper89]

Jeff,

You probably have thought of this but with such a high AH need you might want to look at having two battery banks. You could use one until depleted and then switch to the other. This might help to ration your power system. You could be thinking "Okay, I am on my last battery(ies)". The battery banks might consist of a single battery each, or more than one battery in each bank. Harbor Freight has some inexpensive battery swithches or Blue Sea Systems has some better quality ones. A google search easily turns up either of those. One type of Blue Sea switch will select bank one or bank two, or combine them.

Battery charging is very interesting. There is charging from the tow vehicle that is dependable. You might want to charge one bank at a time while towing, switching to the other bank on a stop. A converter can be very useful for recharging while camping with ground power. I have a WFCO 25 amp model that will recharge my battery and power the trailer at the same time. WFCO also has 35 and 45 amp models. Each includes a power center panel for DC fuses and AC circuit breakers. I am sure there are other good converters on the market, but not all have the fuse/CB panel. I suggest this brand because of my experience with it.
Bill

PS This is a recent topic about battery switches and automatic relays. There are links there to some of the products mentioned.
http://tnttt.com/viewto ... highlight=