Having spent 30 years working with batteries, designing charging
systems and battery
monitors AND referring to electrochemistry textbooks and technical papers regarding lead-acid batteries (yes, AGM's of all types and gel-cell are still lead-acid) it is evident that there is NO set battery
charged voltage that is "correct" with the exception of float voltage (specified at a specific temperature).
Having first-hand experience working with Xantrex, Heart Interface, Trace Engineering and Cruising Equipment
I can tell you that NONE of the "charts" recommending charge voltages came from anyone other than marketing
personell, NOT from electrochemists who design batteries. The marketing
people are forced to attempt to give uninformed users some relevant form of recommendations in order to sell their products.
The basic electrochemistry for ALL lead-acid batteries is essentially the same as far as users are concerned. To be sure there are different chemicals used in the plate "pastes" as well as the plate lead make-up. The formula describing the reversability of sulpheric acid, lead sulphate and lead oxide is the same for all as far as energy transfer (charge and discharge) is concerned. The fact that what is called half-cell equations differ slightly is of no concern as far as how one might charge the battery (at least for the batteries applicability to deep-discharge and high rates of current
charge/discharge is concerned for cruising).
MY past posts describe just how fast one can charge a battery and there are various discussions regarding the so-called "Amp-hour law" taken from electochemistry texts. The three-step charging
algorithm is a first appoximation to the Amp-hour charging method and CAN be exceeded.
There are VRLA (valve-regulated lead-acid) batteries used for things light emegency lighting
that are not designed with sufficiently large plate interconnects to be used for high rates of charge/discharge and are, therefore, limited to charge rates...not applicable to us here where we use batteries designed with large plate interconnects.
None of the charger
or inverter/charger marketing information (that I have read) properly describes just what constitutes a valid equalization
cycle. Equilization is done with a constant-current source that terminates with time qualified by observation of the temperature, cell voltage and charge acceptance. NO manufacturers of chargers have that capability built in and, therefore the marketing people must compromise with a half-baked method which has no where near the efficacy of the proper method. Again, any time that you read what is an "equalization voltage" there is no such thing in the rigorous sense of equalization
Here is a short description of charging: Float voltage is determined by the designed acid concentration and temperature period. There is a simple formula describing the at-rest cell voltage as a function of the specific gravity of the electrolyte. ALL AGM
batteries follow this as well. With ANY lead-acid battery of any type use for deep-discharge high current
applications You can safely charge the battery without excessive temperature rise or gassing by applying a charge current equal to (or slightly greater than..following my experience) the value of Amp-hours "missing" from the battery. This concept
cuts through all of the crap regarding charge voltage because the voltage is always different as the battery comes up to full.
Now when the three-step method was first promulgated by Ample Power
and then by Cruising Equipment
and then implemented by Heart Interface (with their inverter/chargers) it was with the realization that simple voltage regulation in steps could approximate the Amp-hour law. We all wished early on that it was affordable to create a charger
to exactly follow the Amp-hour law yet knew that a battery monitor
would have to be married both to the battery as well as the charger to do that.
in the lab and in the field revealed that ALL of the battery types would respond remarkably well using a true Amp-hour law charging regimen (I did this for years) and that many of the AGM
batteries rejected by many users could be brought back from the dead by using a true equalization method. One REMARKABLE result of doing this is that if subsequent charge/discharge cycles were done using Amp-hour law charging they never needed equalization again as long as they were not left to long in a state of discharge before charging.
One observation that I have made is that the beginning charge voltage of the Amp-hour law charger would always be higher than 14.4V and usually below 15Volts. Does that give anyone a clue? It makes no difference weather
one is using an AGM with a specific gravity requiring a float voltage of 13.2 Volts or one requiring a float voltgage of 13.9 or 14.0 Volts. Gel-cell batteries love this as well and tended to "look" more like the bettery quality AGM's like Fullriver today. Again, do not confuse float voltage with upper limit acceptance voltages that would keep charge current within the limit of the number of amp-hours missing from the battery as stated.
Hope that this helps cut through the crap regarding all the different acceptance or equalization misinformation out there.