Bottom line for batteries is buy the most AH your $$ allow that will fit.
6v are popular because cost economics and abuse factor but the abuse factor is not an issue due to the 12v choice of the OP.
Market economics make the GC2B (T105)usually the most bang for the buck. L16's are also a high volume battery size -if the height is not a problem.
Only time the 6 Vs 12volt question is a real issue is under high amp inverter usage like when a microwave is used for moderate to long time periods. 12v jars handle this condition better than 6v jars in the sizes used by RV's typically.
All of this "assumes" that installation wiring will be adequate for loads imposed.
I like the idea of having 12V batteries in parallel rather than 6V batteries in series. If you lose one of the 6V batteries than your battery bank is dead...
My requirement for my style of camping off the power grid is to do it with around 450AH of battery power and that can be done for around the same price of 6V verses 12V batteries.
I guess you will get more time on-line with the 6V batteries and their long rated time of producing power at a 25AMP rate. Sure has been a well proven battery in the golf cart world...
Just always gets my goat that when you hook up two 6V 225AH batteries in series to get the 12VDC you need for the trailers. Seems to me you wasting one of the 6V batteries. I think I understand all of this but probably dont but if the T105 battery has a 225AH rating at 6VDC then when your connect two togther in series to get the 12VDC you need for the trailer you still only get 225AH of available power. Along the same line if the T105 battery has a capacity rating of 447 minutes at a 25AMP draw then when you connect two togther in series to get the operating voltage up to 12VDC it seems you still also only get the 447 minutes of capacity instead of the 894 minutes at a 25AMP draw you would expect to see. Everytime I look at it I just keep thinking I am wasting one of the batteries...
When you connect two 12VDC batteries in parallel then you can add both the AH rating as well as the capacity in minutes...
Like I say - it seems like you are wasting a battery. The problem of course is finding a 225AH 12VDC battery that you can afford ends up costing a bunch of monies.
I will most likely go with two GP29/31 12VDC batteries connected in parallel which some I have found from Cosco/Sams or Crown battery company are in the 130AH rating range but you suffer some on the capacity rating at a 25AMPS draw... The 447 minutes that the T105 has sure is a hard to beat spec for sure...
Of course on the other hand it sure is a bargin these days to get a SAMs version GC2 battery with almost the same rating of the T105 6V battery for under $100.
My Posts are IMHO based on my experiences - PM me Roy and Carolyn
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Asked this same question at a local RV show of the Trojan rep's.
A summary of his comments:
Both are designed as true deep discharge batteries, but they do offer different performance characteristics and pick the one that best matches your use case.
The 12V was his recomended choice if your drawing heavy current like a big inverter etc. Many big motorhomes use 12V for this reason. The 12V has thinner plates and has lower internal resistance and designed for higher currents. Currents in excess of about 75A/bank. So for two 12V you can draw 150A pretty easily.
12V is also a good choice if your not a heavy dry camper, or seldom draw the batteries down below 60% or so. With the 12V he recomended that you don't recharge them with as high a rate as you can with a golf cart. IIRC he said keep it below C/4 or so.
6V is a good choice if you dry camp a lot, want a large number of charge/discharge cycle life, peak draw <50A or so per bank. So for a pair of 6V golf carts, keep the current in the 50A, maybe 75A or so max. compare that to 150A+ for a pair of 12V. He commented that the 6V golf carts will take hundreds of cycles down to 30%SOC or even 20% SOC. He said just keep them above 20% SOC. Didn't recomend that practice on 12V. The 12V won't last as long, but still will take discharging to 20%SOC occasionally. Also if you want to charge batteries at a very high rate 6V was better.
My case is <50A, dry camp many times, maybe need 50 charges/year, draw down to <50%, often in the 30% range and charge a bank of two 6V @ 90A. (almost C/2)
He recomended I stay with the golf carts.
He said, in either case lack of water kills more batteries than all the rest of the failure modes combined.
As to A/H. be careful. Look at the A/H rate based on your typical discharge rate. A/H is not fixed, it is dependent on current draw. Higher current draw=lower A/H. It can vary significantly from battery type to battery type. In general, 6V A/H tends to hold up better than 12V. Usually the stated A/H is based on 20hr discharge rate, which is often lower than your typical current draw. compare te 20Hr rate and the 30A or 75A rate to see how the A/H rating holds up.
And then consider "usuable A/H". for a 12V figure a 50% discharge maybe stretch to 60% occasionally. for golf carts, you can go to 70% even 80% discharge repeatedly, so for the same A/H capacity, the 6V will give about 20% more useable A/H.
so, see which battery best fits your typical use case.
and, he said they are seeing some folks go to 12V in their golf carts... Why??? well guys that want to "hot rod" the golf cart. The 12V has lower voltage drop under load = more current to the motor= faster acceleration. BUT, he warned, they don't have as much range or life as 6V golf carts!!
Trojan did a good job with the T-105, designing the whole battery around the concept of having enough room to avoid acid starvation. Just about the time when all of you thought the -old harrumph- said his peace, the old harrumph comes back with a new twist, "acid starvation". Acid starvation is the bane of group 29, 30, and 31 batteries. It is a foe of group 65 batteries. It is also a major reason why golf car batteries out live scrubber batteries.
Many battery manufacturers used to report that their 1,500 amp hour 2-volt cells, outlived their 1,645 amp hour cells by more than 10%
So when considering what battery is "equal" to another, simple numbers are not the entire story.