I've done some research and would like to post my findings (although the length may exceed your's JK
. I wonder if you wouldn't mind commenting on it to make sure I'm correct in my understanding.
If a battery is in use, it’s being discharged. And if a battery is sitting idle it is discharging. Sulfation is a by-product of the battery discharging. After a battery discharges, it must be recharged. During recharge, the lead sulfate is reconverted into lead active material and the sulfate returned to the electrolyte. But in order to reverse the sulfation completely, the battery must be recharged completely - to 100%.
If a battery is used infrequently, and then used only for short periods, a 100% charge does not occur and hardened sulfate begins to form. Hardened sulfate also forms in a battery that is constantly being cycled in the middle of its capacity range (somewhere between 80% charged and 80% discharged), and is never recharged to 100%. Most charging sources, engine alternators and battery chargers, are voltage regulated. Their charging current is controlled by the battery's state of charge (SoC). During charging, battery voltage rises until it meets the charger's regulated voltage, lowering the current output along the way. But charging by virtue of voltage measurement is somewhat inaccurate and does not give a true reading of the SoC of a battery. The SoC is also depended upon temperature. A battery voltage of 12.45 volts at 70 degrees is at a different SoC than a battery of the same voltage at 90 degrees. A temperature compensated hydrometer is a more accurate measure of charge, but is somewhat less convenient and only works on wet-cell batteries.
The fully charged specific gravity of a wet-cell battery is 1.270. However, specific gravity cannot be measured on a sealed AGM battery, and a voltage measurement of 12.9 – 13.1 volts is the only way to determine a 100% SoC.
Temperature and/or hard sulfate can make a battery show a false voltage, higher than its true voltage, fooling the voltage regulator into thinking that the battery is fully charged. This causes the charger to prematurely lower its current output, leaving the battery discharged – which propagates additional sulfation. Periodic charging at a higher than normal voltage and low current may be necessary to break down the hardened sulfate.
This controlled charging at higher than normal voltage is called “Equalization”. By equalizing the battery in this controlled overcharge the sulphate coating, is blown off, thereby rejuvenating the battery and allowing all the surface area of the plates to interact with the electrolyte. It also causes the electrolyte to bubble and in wet cell batteries this mixes up the acid and distributes it evenly throughout the cell.
During equalization, the battery should be charged from an outside source at 2.6 to 2.7 - volts per cell (approximately 15.5 volts) and a low current rate (approximately 5 Amps for small batteries and 10-Amps for larger ones) until the specific gravity of the electrolyte starts to rise. (This indicates that the sulfate is breaking down.) Be careful not to let the internal temperature of the battery rise above 125° F. If it does, turn the charger off and let the battery cool. Then, continue charging until each cell in the battery is brought up to full charge (nominal 1.265 specific gravity or higher) or the specific gravity no longer rises..The time needed to complete this recharge depends on how long the battery has been discharged and how hard the sulfate has become.
Although AGM batteries self discharge at a rate 1/5th of conventional flooded batteries, they too will sulfate. And equalizing AGM and other sealed batteries is a bit more tricky. The bubbling electrolyte results in some loss; electrolyte vapor exits the vent caps. However because there is no way to replace the lost electrolyte it is obvious that a different strategy is required. To apply a conditioning charge, first go through the normal charge cycle to bring the battery to full charge. The conditioning charge should then be applied by charging for several hours. At 77°F (25°C), the conditioning voltage should be held to a range of 2.3 to 2.6V per cell (13.8 – 15.6 volts for a 12 volt battery) and the current allowed to vary (electronic pulse). Temperature should be monitored to make sure the battery doesn’t get too warm and cause electrolyte to escape. Some chargers are equipped with selectable settings depending upon whether the battery is a Flooded, Gel, or AGM type – and have temperature sensors that can vary the charge depending upon the type and temperature of the battery.
Once the battery is fully charged, a float charge can be applied. During this phase, the charging voltage is reduced to typically 12.8V to 13.2V (about 2.2V per cell @ 77°F), and held constant at this value to obtain and maintain a fully charged battery state. A temperature sensor feedback to the charger may also be necessary during float charging. As temperatures decrease, voltage may need to increase in order to maintain a full SoC. The effects of temperature and voltage may also differ according to battery type. If a float charger is of a constant voltage type, and the temperature of the area where the battery is charged in is allowed to vary, then it may mean that the battery is being over-charged as temperatures rise and undercharged as temperatures fall. This may lead to the loss of electrolyte if over-charged significantly, or the loss of a full SoC and the resulting sulfation if undercharged for extended periods.
A good charger should have settings for different battery types, voltages and charge functions. As well as a temperature sensor, if charging is not done in a controlled temperature area.
sorry for the length
