Don't know why an offgrid house is brought into this discussion, Pretty much unlimited space in which to house battery banks, solar panels and generators. Not really comparable to a vehicle which must carry everything.
Quote: Id wager the vast majority running on solar sulfate batteries long before they short a cell. I know thats been the case in my old rig for the past 3 sets. Even with 14.8v set absorption. Maybe we should start building banks for a 70% discharge rate to help keep the sulfation down since were killing them early anyway.
The key statement in this paragraph is 'even with a 14.8v absorption.'
The DURATION at which absorption voltage is held, is more important than a few tenths of a volt.
I mean I could apply 150 amps and instantly get a single 50% charged battery to 14.8v. Does this mean the battery is fully charged, and immune to beginnings of sulfation? Of course not. Still going to take no less than 4.5 hours at 14.8v even with 150 amps applied initially to achieve that 14.8v.
2 hours held at 14.8v is better than 2 hours at 14.6 on a deeply dischared battery, but 3 hours of 14.6v is better than 2 hours of 14.8v. Some seem to think that a trojan battery, that specs a 14.82v avsorption set point, is imposssible to recharge fully at any less of an absorption voltage. This is Not true at all. 14.82 will charge faster than 14.6v of course, and cause more water usage, but 14.6v can still complete the task on a still otherwise healthy battery, it just takes longer. Will there be enough time in the day to do so, well 14.82 will stand a better chance of that certainly, should the charge controller allow for that extra duration.
Battery manufacturer recommended voltages have to consider how they believe the majority of their batteries are going to be used, and what recommendations will lead to the least possible number of warranty returns, yet also yield an acceptable life beyond the warranty to develop a reputation. Basically they are second guessing the end user and like everything it comes down to max profit for the fat cat cigar smokers at the top.
i am not saying ignore the manufacturer recommended voltage settings for their batteries, but to understand why they set them where they do. A while back Trojan upped their recommended equalization voltage from 15.5 to 16.2v. Did they do this because they changed the make up of the plates, or because they found that 45 minutes of 16.2v was more effective at maximizing specific gravity and less damaging to those plates than 2 hours of 15.5v? OR did they do it simply because Rolls Surrette has always recommended 16.2v and RS is the Bigwig on the deep cycle flooded battery world?
The 'trick' is to hold absorption voltage long enough so that the battery does reach a true full state of charge, and the more often this happens the longer the battrey will lasty, even with depth of discharges below 50%.
But the deeper the discharges the more important it is to actually reach a true full charge. Lesser depth of discharges are not as damaged by not quite reaching full day after day.
So if one is sulfating batteries prematurely, or what they believe to be so, are they actually checking specific gravity of the flooded cells when their absorption stage is done, or noticing the amperage while the battery is still held at absorption voltage?
The TIME/DURATION as to how long to hold the lead acid battery in absorption is so often overlooked, in favor of the actual absorption voltge number. The time needed in absorption will increase as the battery ages, increase with the depth of discharge, increase with lesser battery temperature, and if only 2 hours at 14.7v absorption are allowed and the battery needs 4.5 hours, guess what, the sulfation destroys the available capacity.
so have all the faith you want in your charge contrller/charging sources ability to fully charge the battery, keep in mind it has NO IDEA the actual state of charge of the battery. the green light indicating full charge is mocking the human who believes it.
Confirm true full charge with a hydrometer, or if with AGM batteries , an Ammeter. 95% of the time the person who seeks to confirm full charge or a marginally or deeply cycled battery, by either method, will find the batteries NOT fully charged, and be stuck with a charging source that inisits that they are, and holds a piddly float voltage at which almost no charging occurs. 1/3 to 1/2 the amps will actually flow into a battery at almost any state of charge, at 13.7 vs 14.7v, and if one is using a 13.2v flooded setting the actual charging occuring is dismally low, and 48 hours of 13.2v will not be able to do what 45 minutes more of 14.7v could have had it been allowed to continue.
Hoping that a float voltage will have enough time to actually fully charge a battery bank before sundown is unwise in the extreme, again proveable by anybody who does not have faith in their product's marketing, and seeks to confirm using a hydrometer or an ammeter with the battery at absorption voltage.
The ability to reach a true full state of charge often and regularly can allow one to dismiss the 50% 'rule'. I am not saying size the battery bank to run it down to 20% each night, just don;t believe that going to 49% state of charge means instant death. it is much easier to kill a battery prematurely by allowing only 2 hours of absorption, when 3.5 are required to reach full charge.
And it is far far more likely 3.5 hours are required on a deeply cycled battery.
Shallow cycling of larger battery banks has different requirements, absorption need not be held nearly as long, and the stock configurations of minimal solar wattage feeding a large minorly depleted battery bank, might be 'just fine'.
I've gone the high battery capacity route with minimal solar, and achieved horrendous battery life, and my van had to carry around an extra 120Lbs of prematurely sulfating battery. No way would I go back to that or recommend others do so on a wheeled platform. Offgridstickandbrickhomessolar.com , do whatever.
Just verify you can achieve and hold absorption voltage for long enough, to regularly be able to achieve a true full charge.