12 volt golf cart batteries do exist, it is just the 6v golf cart batteries are much more prevalent, and probably better, due to a higher volume of electrolyte the plates are surrounded in.
4: Read Sternwake's posts on charging batteries. He cautions us that solar alone is not sufficient for good battery health. Plan on charging by vehicle alternator, and maybe a genset, if you can carry one along.
This really was not my intent nor 100% true. Solar can indeed fully charge batteries, but there is more to it than just replacing amp hours used, if one is trying for maximum battery longevity and actually deep cycling their batteries, daily.
The deeper the cycle, the more solar ratio one should have. fully charging a battery cycled to 80% is a way different animal than charging a battery that is cycled to 50% daily. The deeper the discharge, the more the battery requires higher charging rates, and more time held at the correct absorption voltages.
This might sound obvious, as more energy is required to return a more depleted battery back to full charge, but while a battery cycled to 80% might need 105% the energy taken from it to return to 100% state of charge, the battery depleted to 50% might require 125% of the energy returned into it before the specific gravity rises as high as it can go. These percentages stated are not set in stone, and they will change as the battery ages too.
And I know it is easy to see a flashing green light on a solar controller and assume the battery is fully charged. The flashing green light or any full charge indicator light on any charging controller, Solar or plug in battery charger, DOES NOT indicate the battery is full, it only indicates that the charging source has held Absorption voltage as long as it was programmed to do so. Ideal absorption voltages and durations at which the battery is held there is different for every battery and different as the battery ages, so these one size fits all charge algorithms are more like one size fits NONE.
It might be accurate, it likely is NOT. The deeper the discharge and the more deep discharges in a row, the less likely that soothing and satisfying flashing green light is likely to be anywhere near accurate.
The Hydrometer is the battery state of charge Polygraph. The green flashing light is a freaking liar designed only to make a human observer feel good.
If your Hydrometer proves your blinking green light is not a liar on cycle number 1, try it again in a week of cycling and the odds that it agrees again are much much smaller.
A battery might do OK, and yield an acceptable lifespan as long as the green light flashes daily after a discharge, but it can also just tank in performance, voltage it can hold under loading, while discharging.
My recent flooded battery was one such example. I programmed my controller to the battery manufacturer recommendations, and each day I saw that my solar system had no issues, even in winter, of flashing that green light before 1PM. But after 3 weeks of this, I noticed voltage under load was not impressive at all for a new battery, in fact it was horrible. When I put my hydrometer into the cells I saw 1.225, instead of 1.275 or higher. At that point, i'd used a plug in automatic smart charger, and when it flashed the green light, it was 1.245 on most cells. The next day I programmed my solar controller to go to 15.5volts, and once it reached 15.5 volts, it took more 4 hours( and adequate sunlight)being held at 15.5v before Specific gravity rose above 1.270.
Ultimately I found that 1.285 was the maximum Specific gravity and that 16 volts was the only way to get it that high after it sagged after a number of deep cycles.
That night I discharged the battery regularly, and the voltage held a respectable level under loading. the next day i bumped up absorption voltage and duration, and took a hydrometer reading, again and again, over a period of 2 months before I found what the battery really required when charged only by the Solar, and what it required was well up and above any sane recommendation. 14.9v for close to 3 hours, and then Instead of dropping to a normal float voltage, I had a 15.3 volt finish voltage that the solar held all afternoon long.
Now I am not saying all batteries need this, and I am saying that batteries that do need this are not very good batteries. Unfortunately many 12v batteries Marine or pseudo deep cycle in the group 24/27 and 31 sizes can require these rather extreme voltages and durations when on a low and slow solar recharge, to perform well when the battery is deeply cycled each and every night and solar only recharged.
Now when higher amp charging sources were employed, these extreme voltages and durations were not required to return the battery to 1.275 or higher Specific gravity daily, but if the Solar was the only recharging source, then The controller had to hold the battery at 14.9v for 3 hours once it got there, and then go up a stage to 15.3 for the rest of the afternoon.
Even then it required a 16V equalization charge every 2 to 3 weeks as Specific gravity still walked down cycle after deep cycle.
Now I am not saying everybody with flooded batteries and Solar has to do this same approach. I did so because I have an inquisitive mind and like figuring these things out. Experiment, observe result, change parameters, observe result, on and on as I do seek to at least find what is Ideal.
It is just that 'Ideal' can be SO far from what is 'common' knowledge and retold online over and over. There are a million variables, and what works for one persons system and needs can be at polar opposites of another persons System's needs. Ballpark recommendations are just that, a starting point, and perhaps good enough for some systems, but these same setpoints might behave horribly on the next persons system and usage
The goal is to at least get respectable lifespans from the batteries that are being cycled. Flashing green lights is no guarantee of this, as soothing as they can be.
There are a couple things that can be stated as definites. 1 solar watt to 1 AH capacity is the minimum one should strive for.
Other charging sources, if available, should be employed whenever they are available when the batteries are depleted.
There is no such thing as too much solar. A battery whose solar controller goes into float at 10AM will be a much happier battery than the one whose solar controller goes into float at 2pm. 10 AM is not too much solar. It is not a waste of Solar. it is not a sign of an imbalanced system, It is a marker of a system with happy batteries. When i say float, i am not meaning a premature reversion to float voltages, but that the solar has brought the battery to at least 14.4volts and held it there for at least 2 hours, before reverting to float. Few batteries require less than this, most require more and some much more, when cycled daily.
Ideal chargnig voltages are different for each battery, and the battery manufacturer recommendations are great starting points, but actually getting the battery to full charge, maximum specific gravity, which is required for IDEAL battery longevity, can be a lot different that the manufacturer recommendations.
With Flooded batteries,, and if one cares to maximize lifespan, and seek to approach Ideal, dip a hydrometer when your solar controller goes into float, and you will likely be surprised just how badly that flashing green light has been lying to you.
AGm batteries are much harder to determine how they are responding to any charging source.
Noticing trends and tendencies of voltage under load and amperage required to hold absorption voltages are required for AGM's, If one cares to be a battery nerd seeking ultimate lifespan.
It is far easier to just use the batteries until the day they no longer meet one's capacity needs.
They are, after all, just batteries, and just rented. The length of the rental contract is variable with their treatment.
You can stress it, or not.
Tales of battery longevity, without knowing how the batteries were treated, are worthless.
And internet claims mean nothing. Keyboard Cojones can apparently make anyone an expert in anything.
Often batteries are said to last X amount of years. this is a worthless figure. Now if the batteries are said to have lasted 5 years being cycled 100 times a year to 50%, then this has relevance, but only to the person cycling their batteries 100 times a year to 50% and who uses the same charging sources for just as long.
A full time van dweller requirement of their batteries is MUCH different than the occassional Rv'er. Wel all use different amounts of battery power, discharge them more or less than the next dweller, and the 'Ideal' recharge regimen is different for all of us.
If you seek to approach 'Ideal' then it can be taken to ridiculous levels, and be more effort than it is worth.
Seeking adequate battery lifespan is not very hard to accomplish.
But it is easy to accomplish the inadequate system. Overdischarging and undercharging will have a battery fail to meet one needs, then yield a battery which 'no longer takes a charge' far too soon.
So with solar, plan for more. Hard to have too much
Regarding battery capacity, if you plan to use 50% per night, plan to replace 65% of it by noon the next day, however you can. Solar, alternator generator and plug in charger, or a wind turbine too.
If you never go below 80% state of charge, you have too much battery capacity, 80% of the time or more.
There is a balance, and often recommendations and chosen paths are out of whack with reality.
Beware of 'bragging rights' systems or claims of longevity. Even if the longevity claims are true, they might have absolutely nothing in common with how you plan to use your batteries, and are completely irrelevant, and serve only to confuse, or perhaps sooth, or just boost the ego of the person who made ridiculous claims of longevity.
Trust, but verify. If you go flooded batteries, get a hydrometer and check that lying , yet soothing flashing green light.
Really, the only formulas you need is:
