Some converters are 4 stage with the 4th stage being desulfation at a predetermined interval.
This is not correct. Basically any time you charge a battery it is being Desulfated. Some chargers claim a special desulfating feature which claims to break up hardened sulfate and return it to the electrolyte there by freeing up surface area on the plates and allowing a full recharge. I personally think this is more marketing than actual engineering, though some claim it is effective.
The 4th stage on some converters, which up the voltage to the mid 14's every so often after the converter has taken the battery upto "100%", is intended for DESTRATIFYING the acid on a sitting battery, by causing bubbling every so often, that it mixes up the electrolyte so the stronger acid solution does not seek the bottom levels and become more corrosive to the plates. Just the motion of driving can destratify a battery.
And how many people on this forum actually sit in one place with a converter plugged in day after day that this 'destratification' 4th stage is even going to occur?
Some other misinformation by those in in the marketing department of chargers concern the term equalization.
Equalization is an intentional overcharge of a flooded battery. After many cycles and after a regular recharge, the individual cells on a 12v battery can and will read differently, ie 1.280, 1.290, 1.265, 1.270, 1.270 and 1.275. The equalization, this forced overcharge is an attempt to get all the cell's Specific gravity up to that 1.290 level. This can take hours at 16 volts to achieve, and is pretty hard on the battery, but cells sitting undercharged for a long time is harder on it.
The equalization cycle is kind of like a battery reset. After a proper EQ charge cycle is performed the battery will be at its maximum energy density, however much is remaining. Some manufacturers recommend one every 30 days but this varies. The way to know is with a Hydrometer.
Many batteries that "no longer hold a charge" really just need some lovin Via a good EQ cycle.
My flooded battery needs an EQ every freaking week, and I screwed around with different voltages to do it, 15.2, 15.5, 15.7, 15.9 and guess what, the most effective is 16 volts. I can apply 16v, through my solar every week and get the battery back upto 1.285 on every cell and then it performs nicely. This is with a 14.8 volt acceptance setting and my float setting is 15.1v. Much higher settings than most every charger out there will apply. I use the float as a "finishing" charge, but if I were to stop cycling the battery I would lower float voltage to 13.2v or whatever.
The lower my Acceptance and float settings the lower and lower the SG falls every cycle, and the longer the EQ cycle needed to restore the SG back upto maximum baseline. The 16 volts minimizes the time required to max out the SG. I've gotten it down to 45 minutes. It would take 4 hours at 15.5v. It might not even reach baseline at 15.5v no matter how long it is applied.
But 16 volts is too high for most 12 volt electronics, so an EQ should be performed with vehicle cables removed from batteries.
Do Beware of any claims and features by charger/converter companies. Their marketing departments have a bunch of clowns in it that have no idea what a battery actually requires to reach full charge. Automatic chargers primary function is to NOT OVercharge a battery. They all use different algorithms to achieve this planned undercharge, and will make such and such a claim and try to impress possible consumers by adding another "Stage". Well a 4 stage charger has to be better than a 3 stage charger right? ha. Some chargers out there have battled their way up to 8 stage charging. Perhaps we should get together and market a 10 stage charger and make millions.
Most automatic battery chargers stop charging well before the battery is indeed fully charged. That blinking or solid green light seems to release enough serotonin in the brain of the user that they are convinced their purchase was justified and their confidence in the product is justified. Dipping a hydrometer into the flooded battery whose charger is flashing that green light would be a slap across the face of such a person.
The charger most capable of maxing out the SG on any flooded battery is a single stage manual battery charger, but it is not automatic. There are no blinking green lights. The user has to monitor the battery voltage and the Specific gravity, and battery temperature and know when to turn off the manual charger.
Eq cycles should be performed when the SG of the cells varies by more than 0.015., and only after the regular charging source has given up and thrown on the magical serotonin releasing yet lying SOB flashing green light. Enough amperage should be applied to quickly raise the voltage to 16v. The formula for this is 5% of the amp hour capacity measured at the 20 hour rate. So 5 amps for a 100 amp hour battery. 16 volts should be applied until the SG stops rising or battery temperature starts rising. More than 120 F is the rule, but in general this is reaching uncomfortable zone, but the higher the temp the better the chance the EQ cycle will revert hardened sulfate back into the electrolyte and restore lost capacity.
When I do an EQ cycle, I start it after my Solar has taken the battery upto 14.8 volts and the current required to hold it at 14.8v has dropped to 0.8 amps. My controller then goes to 15.1 volts and usually 1.2 to 1.8 amps is required to hold this voltage. I then pop the cap, dip the hydrometer and will see anywhere from 1.220 to 1.270. I then move all my loads to my other battery, readjust my Acceptance and float voltages upto 16 volts and it will take 6.2 amps to raise and hold the battery at 16v, which is right around 5% of the 130 amp hour capacity.
SG will take anywhere from 30 minutes to 4 hours to climb back upto 1.285 on all cells. by the enmd of the EQ cycle, when SG has stopped rising, the amps required to hold 16v have tapered to the 3.2 range. After an EQ cycle, that night, the battery performs admirably, in terms of voltage held for the loads placed on it.
This is a strange battery and most Flooded batteries should not require a weekly EQ cycle but figuring out what the battery requires to reach maximum energy density has little to do with the blinking green light, or claims by the charger manufacturer and the only tool out there which can let you know this is a Hydrometer. Watching a voltmeter closely and noticing that the battery seems to lose voltage more quickly than before can be a sign, but the only way to Know is with a Hydrometer.
Now this may seem like a lot of effort to go to. It is, but relying on a plug and play charger to properly tend to any specific batteries is like drinking the Kool aid.
It might not be worth the extra lifespan that providing a more aggressive properly monitored recharge regimen can provide.
After all, batteries are only rented.
Armed with this knowledge, you can decide how far you care to go to max out battery lifespan and performance during that lifespan. But whatever you do, do not fall into the blinking green light stupor that so many do. Blinking green lights mean little. It is more indicative that the technically clueless lawyers and the bean counters and marketing department have overruled the engineers once again.