EQ alization charges are abusive to a battery.
They should only be performed when it is obvious the battery is under performing, or when it is known it sat undercharged for a long period of time.
They should only be initiated after a regular 'full' charge has been completed.
Ideally, They should only be performed when the end user has a hydrometer, and the ability and desire to use it/ monitor the process and terminate it when the objective has been reached..
If the cells cannot be accessed then one needs to more closely watch its temperature, and hopefully has a way to monitor not only voltage, but the amperage the battery is accepting at that voltage, and terminate charging once the amperage to maintain voltage bottoms out, and then starts rising again.
AGM or Gel batteries should not be equalized, with the exception of Lifeline AGM batteries, though they call it a 'conditioning'.
Battery makers and charger/ voltage regulator solar charge controller marketers like to use some conflicting terminology regarding stages of charging.
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The EQ charge should be ended immediately when specific gravity stop rising, or battery temperature starts rising rapidly. If temperature rises rapidly and specific gravity is still well below expected, allow battery to cool to below 80F, then try again.
Lead acid batteries are generally quite tolerant of the occassional minor overcharge, but starting batteries are pretty fragile, compared to marine or actual deep cycle batteries when exposed to these voltages.
EQ voltages Spec'd by the big names in deep cycle lead acid batteries, Rolls Surrette, and Trojan, are 16.2v. These numbers assume a battery temperature of 25c or 77f.
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When I was daily deep cycling a flooded marine/dual purpose 12v battery, the hydrometer revealed how poorly my regular recharging regimen was doing.
I had to up the absorption voltage and its duration, and still, specific gravity walked down each 'full' charge as did voltage retention during each subsequent discharge.
Every ~14 deep cycles an EQ charge was performed to get specific gravity up to 1.275+ in all cells
In the beginning this was taking close to 4 hours at 15.5v.
I tried 16.2v and it took under 40 minutes.
A stayed with 16.2v after that.
Its good to know the maximum specific gravity when one acquires a new battery and has fully charged it, for later comparison. but one actual cycle is usually required as off the shelf uncycled batteries behave weirdly whether they sat on the shelf for 1 hour or 1 month.
OTC 4619 is a good hydrometer with a thermometer that says how much to add or subtract from the reading on the float to account for electolyte temperature. The curved plastic ones and similar have poor accuracy, precision and repeatability, in my experience, and the floating ball ones are not worth the 99 cents they charge for them.
Its good to have a charger which can bring the battery to 15.5v, intentionally.
Some chargers will do so when it is not required. Bringing a less than fully charged battery to 15.5v with high amperage is much more abusive, than bringing it there with lesser amperage after it has gone through a normal 'full' charge cycle. Schumacher 'intelli' chargers should be monitored closely for this potentially abusive and unpredictable behavior. My sc2500a would bring an 85% charged battery close to 17 volts on the 12 or 25 amp setting, but was less likely to do this on the AGM setting at 12 or 25 amps.
Flooded lead acid batteries self discharge anywhere from 5 to 15% per month. More self discharge at higher average temperatures, lesser at lower. The self discharge is affected by battery health. They self discharge faster with more age/less health and when non distilled water is used to refill them, or contaminants are allowed into the cells when filling them, which can be hard to avoid without busting out the Q tips after removing the cell covers carefully.
It takes no less than 3.5 hours to charge an 80% charged battery to 100%, no matter how powerful the charging source might be, or how impressive its marketing might be.
The less healthy the battery, the longer 80 to 100% takes, and a true 100% might not be possible without EQ voltages and this is more and more true as the battery ages or is subjected to abuse, such as overdischarging or living its life chronically undercharged..
Those without a hydrometer cannot know when a true 100% state of charge has been achieved.
The green light on a smart charger only indicates the charger has decided to switch to float/maintenance mode.
It has no special powers to enter the battery and read the specific gravity of the 6 cells, and detect when a true full charge has been achieved.
The true full charge achieved regularly can greatly extend the life of the battery, but good enough is subjective, opinion, and the effort of attaining true full charge can be considerable, and perhaps not that important in a engine starting battery when a new one is easily enough obtained.
A hard working deeply cycling battery requires that regular true full charges are promptly achieved, or it loses capacity and become harder and harder to recharge to its maximum remaining capacity, which then accelerates the capacity loss. The regular 'smart' chargers sold for occasional garage use, fall well short on the hard working deep cycling lead acid battery, whether Flooded AGM or GEL. Such chargers should be well ventilated, and when they flash the green light, skoff, drag battery voltage to below 12.8v with a large load, like the headlamps and blower motor, and restart the charger then remove loads.
This might or might not work to further raise specific gravity towards its maximum. Tricking the smart charger over and over gets old quickly.
Best to remain ignorant that it is not performing the true full charge, especially when obtaining and replacing the battery is no big deal to the owner.
If one reads and grasps the info in the Rolls Surrette/ Trojan and Lifeline owners manuals, they will realize much of what they though they knew, was wrong.
