Lifepo4 can be killed too, and is much more expensive to replace.
Float charging is a Bull **** stage that has confused you. Float is for when batteries are fully charged, to keep them fully chrged. NO actual charging should be occurring during float. If more than 0.4 amps of current are flowing for each 100Ah of battery capacity at float voltage, then the absorption stage was not long enough and blame the charging source for prematurely reverting to float voltage, and apologize to the battery.
'Trickle charging' is a term right wing battery idiots use as it sounds good to their ear, as grandpa used to say it frequently, but grandpa knew nothing about battery charging either.
In full time RV dwelling with a heavy electrical user, there are two battery charging stages, Bulk and absorption. Only those with excess solar and minimal battery consumption will ever need the float voltage stage.
Say a golf cart battery is rated at 1200 cycles. This means that if they actually tested them, it would discharged exactly to 50%, and recharged over 8 to 12 hours to truly full, then cycled to 50% again. They estimate the battery will be able to do this 1200 times before its capacity is reduced to 80% of that when it was new. These are lab cycles. NO ONE, in actual use, achieves lab cycle numbers, not at 50% depth of discharge. no way.
Batteries die, your estimation of having to replace them 2 to 3 times in 2 years is extremely premature, and perhaps wildly incorrect. Even if true, replacing flooded golf cart batteries 2 to 3 times in 2 years, will still be substantially cheaper than setting up a proper functioning Lifepo4 system now.
Unless you have ventilation issues, do not get AGM for this task as they are more needy of the 100% recharges, and achieving those at higher amperage rates than flooded golf cart batteries. people tend to put the Superbattery status onto AGM because of the price, but they are more finicky when not treated to a full charge more regularly than their flooded deep cycle counterparts. Flooded golf cart batteries are the most forgiving, best bang for the buck battery available.
With hard working lead acid batteries, sometimes one just needs to lay off the electrical usage one day before a known sunny day occurs, and get to and achieve absorption voltage ASAP the next morning, and hold it all day long, perhaps bump up the solar controller settings to 16.2V after 4 hours at absorption.
Will this be enough to maximize specific gravity on all cells? perhaps, perhaps Not, but the attempt will be much appreciated by the batteries.
Perfect recharging is nearly impossible to achieve, outside of a laboratory. Inability of the user to achieve the occassional perfect recharge, is standard. That you know that the batteries will not be happy being worked as hard as you intend on working them, puts you way ahead of most with an RV.
I just replaced 2 of my neighbors 100$ wally world group 27 marine batteries with 2 84$ golf cart batteries(210AH) from Costco. These are interstate branded batteries, and at this moment in time, in this location( S california) are apparently made by Trojan, and correlate to the Trojan T-605, which is a few steps below the venerable t-105.
The trojan T-605 weighs 58Lbs, the t-105 weighs 62Lbs, the t105RE weighs 67Lbs. Heavier mo bettah.
Costco is wonderful about warrantying batteries, even those killed by intentional or unintentional abuse.
Get 4 or 6 of these and see how long you can make them last in your usage. You might be surprised at how long they can handle your abuse, and you might be able to get a new set under warranty.
My neighbors rig's batteries last about 2 years, as he simply does not care about the batteries. Runs them dead as a doornnail when not plugged in, thinks a short drive is more than enough to fully charge them, and does not bother pluggin in the rig when at home. And does not listen, as he does not care.
I do not expect these golf carts to last any longer in his usage, but they were at least 16$ less per battery, and with Costco, he can likely kill them and warranty them for the price of a trip to costco.
No doubt Lifepo4 is a superior battery, but they have all sorts of parameters they must remain within, and can be killed quickly, if allowed outside those parameters. Lead acid is much cheaper and more forgiving of the time they spend outside their parameters.
The 12 hour absorption stage of a hard worked lead acid battery you quoted, is an extreme example with a very hard worked battery well past the half way mark in its lifespan, that should not be used as a reason to disregard lead acid all together.
People who really work the piss out of their batteries, and see their solar controller in float by midafternoon, should raise float voltage to the same as absorption voltage.
It is the premature reversion to a low 13.2 to 13.6v float voltage which is the main lead acid battery killer.
Enough solar to get there and hold it there makes for pretty happy batteries.
When more is needed than 760 watts, consider a portable panel to bust out and aim at the sun a few times per day. The earlier one can achieve absorption voltage, the happier the battery. An Unhappy battery bank should be given a light overnight load before a known sunny day, and allowed to achieve Absorption voltage ASAP, by whatever methods available.
When mine is due, Since I can plug in, or drive to get 65+ amps into my well depleted battery, I actually intentionally drain my AGM even deeper, and apply high amperage before my solar has had the chance to do the low and slow thing. 30 to 60 minutes of high amperage in the early morning from its most depleted state, and 200 watts of solar all day long holding absorption voltage, makes my battery have an orgasm.
This AGM however has no upper limit on charging amps, well no amperage I can achieve anyway.
A rig with 4 or 6 hard worked gasping GC-2 batteries, I would start the engine and drive for an hour or 2 near sunrise, with a thick copper circuit between alternator and house battery, then the solar should have no problem holding Absorption voltage as long as required, and should be able to reset capacity to the maximum remaining potential. This need not be done several times a week. Once every 10 days to 2 weeks will significantly extend the lifespan of the batteries.
But factor in the cost of gas for driving for 1 to 2 hours, if not having to go anywhere otherwise. Could be cheaper to simple replace batteries more often.
