The thing with 6v flooded golf cart batteries, is that they were designed around deep cycling and resistance to degradation from less than proper recharging. A 12v marine battery could be drained dead and left for a week or two discharged and be permanently damaged fro such abuse. Whereas a pair of 6v batteries in parallel, all factors being equal, could very well 'take a charge' and still give respectable performance afterward.
ALL 12v batteries, no matter how well they are marketed, with 'DEEP cycle' prominently displayed on the sticker, can not ever compare to the ruggedness of a pair of 6v Golf cart batteries in deep cyclic applications. The Trojan T-105 6v golf cart battery sets a benchmark in cycle life and resistance to abuse, and while more expensive than other 6v GC batteries, all it takes is one semi miraculous recovery to abuse which sets the substandard and the benchmark battery apart, making the benchmark significantly cheaper battery to purchase in the first place.
Sam's club, and Costco carry 6v golf cart batteries and a pair of these in series are Superior to a set of 12v batteries of equal capacity, but they are also not in the same league as Trojan T-105 or Crown or USbattery GC-2 batteries, Or East Penn Deka.
Very Few 12v batteries are built anywhere near as durable 6v batteries in deep cycle applications. Even the 'true' 12v Deep cycle batteries, of which there are terribly few and these few are terribly pricey, will have only half the rated cycle life as a pair of t-105's, and only if they are recharged promptly and properly.
The golf cart market is where the big4 battery manufacturers goto war against each other Any clear winner here in this market can easily take over the market share, So they compete. the ^v golfcart battery market is where the manufacturers will expend all their efforts into a winning battery. The 12v batteries they sell with deep cycle stickers are a complete joke in comparison... they make them only because there is a market for them, but it would take a drunk applications engineer( marketer) to admit that any 12v battery can hold a candle to a 6v battery, and they'd recant in the morning and hope to heck they are not fired before lunch.
AGMs are a legitimate crossover battery capable of High CCA ratings and also claim resistance to multiple deep cycles, however the AGM's have less tolerance for less than perfect recharging.
If you can meet the AGM charging specs, they can be awesome. Generally, AGMs want higher amp recharges they thrive on higher amp recharges, well and above what most Solar only recharge regimens are capable of . The maximum Absorption voltage varies a bit brand to brand. If you cannot meet them, then they can be a very expensive battery that was killed in the same time as the least expensive battery. Often people equate price with the ability to be ignored. Odyssey, Northstar and Lifeline have ridiculously expensive batteries. they are extremely capable batteries, when recharged properly, but improperly recharged, they become expensive paperweights all too soon. And the purchaser of such a battery expects their price to impart immunity to owner abuse. Such consumers are the most vocal, but the blame lies in the mirror when premature failure occurs.
Battery life is directly proportional to the recharging regimen's efficacy. 6v flooded golf cart batteries are easier to properly fully recharge, no matter how vociferous the 12v proponents get, and they can get obscene when questioned or doubted, or just need a soothing agreement from a fellow 12v user.
There is no one right answer to any of this, but many wrong answers. Optimistic paranoid did not type anything I disagree with, and I thank him/her for summing it up nicely.
The trick to a well working electrical system is to charge the battery back to 100% as often as possible and as soon as possible, and prevent discharging the battery below 50% State of charge regularly.
Do this and you can expect acceptable battery life. Ignore this minimum and you will pay for it, with new batteries, replaced prematurely, an aggravation to spare.
Solar is great for the 80 to 100% recharge, but , other higher amp charging sources applied early enough so that the solar can easily do the 80 to 100% thing from late morning to sundown and earlier, really makes for a happier longer lasting battery.
It really sucks when the battery just noticeably walks down in overall capacity every cycle. Only those with an Ammeter or who observe their voltmeter religiously under discharge will ever notice any aberrations. The rest love the head in the sand ostrich approach, and seek comfort in numbers, and they readily find it.
It works 'just fine' until the day it does not. 95% of battery dischargers froth their way to the 'just fine' delineation with absolutely no understanding until the day when their battery capacity is no longer 'just fine' to meet their needs, or the battery shorts a cell way to early in its life.
If you need at least 210 AH of battery, you are wise to get 6v golf cart batteries as opposed to any 12v battery. Every 12v battery is a compromise. Every 12v battery ,but a seldom few, was designed to be a drop in replacement for an automotive starting battery. As such, they cannot compare to the 6v golf cart battery which was designed for a specific purpose, which is deep cycling.
Do not believe the marketers, or the marketing. If you want a battery capable of resistance to user error and improper care, the 6v battery will pay for itself compared to the person buying a pair of group 31 12v 'deep cycle' or marine batteries of nearly the same capacity.
It is also easier to fully charge a set of 6v golf cart batteries than it is a pair of 12v batteries. 12v batteries tend to need higher absorption voltages applied for longer to reach a true 100% recharge, and if they do not get this, then the next discharge they only have 95%, then 90, then 85, and so on, until at one point the human observer notices that batteries' no longer take a charge' and only then go through the increased effort required to maximize the specific gravity across all cells, and this can require chargers than can bring the battery to and hold it at 16 volts. Such a charger is a rare bird indeed.
At such a point the 12v batteries need some serious loving( 4 hours at 14.8v or higher) to return to anywhere their 'new' rated capacity, where as the 6v batteries will take half the effort and start calling you the sissy. "You call that a Knife?"
If you can accommodate the extra height requirements of a pair of 6v golf cart batteries in series, but instead opt for 2 of any 12v flooded battery in parallel, you should check yourself into the mental hospital, as you'll be essentially paying nearly twice as much for half the battery lifespan, all factors being equal.
CCA ratings mean diddley squat in a deep cycle application.
Positive plate thickness is the deciding factor in Deep cycle applications.
Trojan t-105 batteries have thick robust positive plates and as such they are the benchmark cycleable flooded battery, and their initial cost increase, will cost less in the long run, the only exception is for those who were desitined to kill a battery ASAP by chronic undercharging an ignorance that a lead acid battery cannot be left discharged until convenient for the human to recharge it.
Lifeline AGM batteries have by far the thickest positive plates of any AGm battery. Only a few true deep cycle batteries even bother with CCA ratings, and only do so because of consumer uproar and ignorance. In fact of two batteries rated at 100 Amp hour capacity, the one with 700 CCA will fare much poorer than the one rated at 600CCA in deep cycle applications. One can almost determine the thickest positive plates by the lowest CCA numbers. The Lifeline group31 T batery has 105 amp hours and 600CCA. the Odyssey group31 has 1150CCA and 100 amp hours. In the same deep cycle application, the lifeline should deliver 2x total number of cycles. However the Odyssey will always crank the engine faster
Setting up a System initially, one should seek to incorporate 6v GC batteries if possible. They are by far, the best bang for the buck. Those of us stuck with a single 12v battery, have acknowledged the fact that no single 12v battery, no matter how well designed and constructed and marketed, can compare to the 6v Golf cart battery in deep cycle applications.
My Next batter will be the Trojan T-1275. This is a 'scrubber' battery, and almost on Par with the Trojan t-105, but this is one of the only 12v batteries which comes anywhere near the 6v T-105 standard for resistance to sub optimal charging and abuse.
I have no faith in Wally world batteries. Johnson controls, who make WW batteries, is not well known for anything but starting batteries, and their dual purpose marine batteries do not do well when treated as a deep cycle battery, so while Wally worlds are everywhere and you can kill one of their batteries and pay for a pro rated replacement, often there is no money saved and a lot of aggravation added when the petulant battery' no longer takes a charge'
