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F4Gary · 03-10-2015, 12:32 PM

If you decide to go AGM, do not get an Optima battery. They haven't been worth a darn since Johnson Controls bought them about 5 years ago.

vettenuts · 03-10-2015, 05:44 PM

I didn't think that the charge and maintenance cycles for lead acid and AGM were the same. That being the case, wouldn't the OP need to find out what charging cycles his onboard system can handle?

rssnape · 03-10-2015, 06:01 PM

I went from 4 12V batteries group 24 to 3 12v group 31 batteries and now have more AmpHour capacity in my bank. Look for what physically fits in your compartment and try to maximize your total AH capacity.
Obviously if you go with 6v you will need to do them in pairs.

If access to them will be difficult for adding water, a watering system or switching to AGM's may be necessary.

1997 Tiffen Allegro Bus 37', Cat 3126

GREGORYJ · 03-10-2015, 06:31 PM

I replaced my 8 years 2-6V. Trojan T-105's with 2 -12v. deep cycle marine batteries and after 2 years where not performing well, barely make it though the evening watching TV. I had to replace them and went back to 6 V. GC type batteries from Costco. Similar weight as the Trojan T-105's (68 lbs each). Three years later they are still preforming like new. If you go with these, check your battery compartment space, especially for battery height , and during use check water level every few months as already mentioned.

Mr_D · 03-10-2015, 07:00 PM

Quote:

Originally Posted by Gary RVRoamer

The voltage has nothing to do with it - it's the battery type and size/capacity that is important. And cost, of course. The "6v" that RVers refer to is the GC2 "golf cart" battery and they yield about 230 Amp-Hours per pair and typically cost around $120 each. A pair of 12v deep cycles in size Group 29 or 31 will deliver about the same amp-hours but typically cost much more, maybe $170-$200 each. GC2 batteries are produced and sold in high volume, so the pricing is usually better than the 12v deep cycles (which are a low volume specialty item).

AGM technology is excellent for a deep cycle battery but it's main advantage is low maintenance. It actually has a bit lower amp-hour capacity than a flooded cell deep cycle. And the price premium is usually substantial. However, if you are the type that forgets to maintain your flooded cell batteries, the extra up-front cost of an AM may pay off in the long term with extended battery life. The flooded cell will die of neglect while the AGM keeps on going.

I've written an article on Choosing the Right Battery for Your RV - it is available HERE.

Our new to us CC Magna has 4 1000 CCA cranking batteries and 4 8D 12 V AGM batteries. Need to replace them all soon. The inverter/charger can only be set for one type of battery so the starting batteries are supposed to be AGM's also. But I think they're sealed cell, low maintenance ones. All of them are original ones so they're 6 yrs old and showing their age. The AGM batteries may be the greatest ever but I'm not convinced since I got 10 years out of my U-2200's in the Dutch Star with the same brand inverter/charger.

Mr_D · 03-10-2015, 07:02 PM

Quote:

Originally Posted by GREGORYJ

I replaced my 8 years 2-6V. Trojan T-105's with 2 -12v. deep cycle marine batteries and after 2 years where not performing well, barely make it though the evening watching TV. I had to replace them and went back to 6 V. GC type batteries from Costco. Similar weight as the Trojan T-105's (68 lbs each). Three years later they are still preforming like new. If you go with these, check your battery compartment space, especially for battery height , and during use check water level every few months as already mentioned.

Marine batteris are not a true deep cycle battery no matter what the company advertises. They are a compromise on both starting and house use. Not a good choice for house batteries at all as you found out.
And putting mineral oil in each cell will stop most of the distilled water adding and possibly add to their life, they did to mine. The mineral oil is an old trick that the railroads used to cut down on maintenance. 2 oz in each cell for 12 volt and 4 oz in each cell for 6 volt seems to be about right.

isa · 03-20-2015, 12:54 PM

If space is limited, forget about 6v batteries and go with two 12v 31DCF AGM's. They will give you the best value. No corrosion since they are self contained and if one battery fails you are not dead in the water since you still have another. Neither of these statements is true with respect to 6v batteries.

wa8yxm · 03-20-2015, 01:32 PM

The problem.."2 12 volt batteries" means nothing..
Some info

Batteries for the most part are
Flooded Wet Cell
Maintenance Free
AGM
Optima (Not recommended for use as house batteries)

You will also hear reference to "GEL" from time to time...Forget those. OPTIMA advertises as both GEL and AGM..(They are AGM) thus causing confusion.

Optima,due to the sprial design have at most 2/3 the capacity of same size other lead acid batteries,,,and cost more..hence the not recommended

Flooded wet cells, if properly maintained are the least expesive and work well.. IF NOT maintained, they fail swiftly

Maintenance free, which includes AGM and Optima need very little maintenance but...This means you can not extend their life by properly maintaining,,,,plus they cost more.

Within each of those designs you can get

Starting
Marine
MARINE/deep cycle
and DEEP CYCLE

(Case is important in the above list)

Starting batteries are designed to deliver a lot of amps.. But only a tiny amount of their total charge (perhaps as little as 10%)

DEEP CYCLE, can safely go to half full, but not nearly the peak amps

(marine are starting batteries but rated for peak amps at 0C, where as starting are rated at 0F)

MARINE/deep cycle, can go a little farther down but 50% is too low.

Some sizes

GC-2, is a 6 volt golf car battery, True DEEP CYCLE 230 amp hours Put two of them in series you get one 2-piece 12 volt battery (Equal to a 4D) Treat them as such and you will be very happy.

GC-12 is about 150 amp hours..12 volt,, also DEEP CYCLE
(The GC stands for GOLF CAR)

Group batteries
Group/Amp hours each
24/73
27/95-100
29/100-110
31/130
8D and 3d Are in the 200-250 amp hour range

And there are others as well.

Why are GC-2's so popular?
Half the weight of a 4D but when you pair them they equal a 4D means it is easier to wrangle them... But even more important is this.

Golf courses from the Atlantic to the Pacific and beyond order these things by the pallet load.. it is the single most produced lead acid rechargable..This means it costs less.

Davidej M · 03-21-2015, 11:25 PM

You should probably go to a battery explanation site to learn the difference between house batteries and starting batteries. The demand on each is different and the construction of the battery is different. The two batteries you described as being your house batteries (31's) are starting batteries and not designed for use as house batteries.
To keep it simple use groups of two 6 volt golf cart batteries wired in series giving you 12 volts and then these groups of two should be wired in parallel.
I hope this helps