The first stage in a 3 or 4-stage CC/CV AGM battery charging algorithm is the “Bulk Stage.” The Bulk Stage is a “Constant Current” (CC) charge but may also be Constant Power, Pulse Current or Taper Charge.

In this BULK charging stage, the current should be limited to 20% to 30% of the battery C₂₀ Ah rating. The Bulk Stage is a “Constant Current” (CC) charge but may also be Constant Power, Pulse Current or a controlled taper current Charge.

In this first BULK charging stage, the optimum charge current should be limited to 20% to 30% of the battery's C₂₀ Ah rating. This stage should end when the cell voltage equals 2.45 volts per cell +/-.05 volts at 25°C/77°F.

This stage will represent approximately 60%-80% of the total charge time. The battery will be nearing 95% state of charge at the end of this stage.

The second stage is the “Absorption Stage.” This stage is a Constant Voltage (CV) stage where the terminal voltage is maintained at 2.40 V/Cell +/- .05 volts per cell at 25°C/77°F (remember to temperature compensate this voltage if possible).

The charge current is maintained until current acceptance drops by less than 1 ampere over 1 hour. This stage should take the battery thru 100% SOC and comfortably achieve its required overcharge of %104% to 112% of the previously discharged amount.

The total charge time thru stage 2 should not take longer than 10-12 hours. If this time is exceeded, charging should be stopped, and the battery, charger and/or charge process should be analyzed.

The maximum time in hours should = 1.2 times the Depth of Discharge (DOD) in Amp-hours (AH) divided by the average charge current in amps. If this time is exceeded, charging should be stopped, and the battery and/or charge process should be analyzed.

The process of charging a battery can reasonably be considered complete when:

• the batteries voltage does not continue to rise and remains stable over a measured period (voltage wins over time), or
• charging current drops by less than 1 amp over 1 hour (time wins over-voltage)

The third stage is the “Float Stage,” or the maintenance and monitor stage. This step is generally not needed if no load is present when the battery's device is not in operation and the battery's device is used regularly. It does not sit idle for lengthy periods. Float voltage should be maintained at 2.27V/Cell.

If a “Balance Mode” is included in the charging algorithm, it would follow the Absorption Stage and precede the float stage. This would become the third stage, and the “Float Stage” would become the fourth stage. A balanced mode is similar to an equalized function for flooded batteries but is performed at a lower voltage and/or is tightly controlled against current, voltage and time.

Compensation for temperature above or below 25°C/77°F can be made by:

• Subtracting 0.005 volts per cell for each 1°C (0.003 volts per 1°F) above 25°C or,
• adding 0.005 volts per cell for each 1°C (0.003 volts per 1°F) below 25°C 

WARNING – DO NOT EQUALIZE CHARGE GELL OR AGM BATTERIES! Equalizing is an “over voltage-over charge” performed on flooded lead-acid batteries after they have been fully charged to help eliminate acid stratification. It helps to eliminate the acid stratification and sulfation that happens in all flooded lead acid batteries. Acid Stratification is the #1 killer of flooded lead acid batteries.

Laboratory-designed, specific to Discover, “Balance” charge algorithms have been designed. They are included in all Discover recommended Industrial Commercial charges offered for sale wherever our Discover AGM and GELL VRLA DRY CELL products are sold. Visually the Balance Charging curve diagram is similar to a flooded equalize charge curve in its finishing voltage. Still, it is strictly controlled to promote proper active material conversion and not to promote gassing or bubbling of the acid to help reduce acid stratification as in a flooded battery. Discover^’s Balance charging algorithms are HIGHLY recommended for batteries being installed in strings, larger batteries using taller plate groups and/or with batteries constantly being subjected to high-rate deep discharges

The first stage in a 3 or 4-stage CC/CV GELL battery charging algorithm is the “Bulk Stage.” The Bulk Stage is a “Constant Current” (CC) charge but may also be Constant Power, Pulse Current or controlled taper current Charge.

In this first BULK charging stage, the optimum charge current should be limited to 15% to 20% of the battery's C₂₀ Ah rating. This stage should end when the cell voltage equals 2.35 volts per cell +/-.05 volts at 25°C/77°F.

This stage will represent approximately 60%-80% of the total charge time. The battery will be nearing 95% state of charge at the end of this stage.

The second stage is the “Absorption Stage.” This is a Constant Voltage (CV) stage where the terminal voltage is maintained at 2.35 V/Cell at 25°C/77°F (remember to temperature compensate this voltage if possible).

The charge current is maintained until current acceptance drops by less than 1 ampere over 1 hour. This stage should take the battery thru 100% SOC and comfortably achieve its required overcharge of %104% to 112% of the previously discharged amount.

The total charge time thru stage 2 should not take longer than 10-12 hours. If this time is exceeded, charging should be stopped, and the battery, charger and/or charge process should be analyzed.

The maximum time in hours should = 1.2 times the Depth of Discharge (DOD) in Amp-hours (AH) divided by the average charge current in amps. If this time is exceeded, charging should be stopped, and the battery and/or charge process should be analyzed. 

The process of charging a battery can reasonably be considered complete when:

• the batteries voltage does not continue to rise and remains stable over a measured period (voltage wins over time), or
• charging current drops by less than 1 amp over 1 hour (time wins over voltage)

The third stage is the “Float Stage,” or the maintenance and monitor stage. This step is generally not needed if no load is present when the battery's device is not in operation, and the battery's device is used regularly. It does not sit idle for lengthy periods. Float voltage should be maintained at 2.25 V/Cell.

If a “Balance Mode” is included in the charging algorithm it would follow the Absorption Stage and precede the float stage. This would become the third stage, and the “Float Stage” would become the fourth stage. A balance mode is similar to an equalize function for flooded batteries but is performed at a lower voltage and/or is tightly controlled against current, voltage and time.

Compensation for temperature above or below 25°C/77°F can be made by:

• Subtracting005 volts per cell for each 1°C (0.003 volts per 1°F) above 25°C or,
• adding 0.005 volts per cell for each 1°C (0.003 volts per 1°F) below 25°C 

1. Only charge AGM or GEL batteries using a genuine and reliable temperature-sensing voltage-regulated charger.
2. Never use a constant current charger without voltage regulation!
3. Charging Current or Amps is the flow of electricity. Every battery can only store, deliver or receive a certain amount of electricity. Voltage is electrical pressure. The amount of voltage dictates the rate at which the amps will flow into the battery during the charging process. The temperature at which this process is taking place also affects charging. When the correct pressure is used at the right temperature, the battery will be charged at its optimal rate. If too much pressure (wrong voltage settings) is used, excess current or charge will flow through the battery than it can absorb. This will cause the battery to gas and generate hydrogen and oxygen faster than it can be recombined. This will lead to the destruction of the battery.
4. GEL batteries maintain absorption charge voltage at no more than 2.35 +/- .5 volts per cell and float voltage at no more than 2.25 volts per cell at 25°C/77°F.
5. AGM batteries maintain absorption charge voltage at no more than 2.45 +/- .5 volts per cell and float voltage at no more than 2.27 volts per cell at 25°C/77°F.
6. Compensation for battery temperature above or below 25°C/77°F can be made by:
   • Subtracting005 volts per cell for each 1°C (0.003 volts per 1°F) above 25°C or,
   • adding 0.005 volts per cell for each 1°C (0.003 volts per 1°F) below 25°C 
7. When charging, consider that to replenish the ampere-hours removed in the discharge process adequately, you will need to replace 104% to 112% of the charge removed for AGM and GELL batteries.
8. The time it will take to charge will depend on certain variables such as the depth of the discharge, the ambient and battery temperature, the age/condition of the battery and the charger's overall features. Typically, you should expect that it will take 60%-80% of the charge time to return the battery to within 95% of its original capacity. It will take the remaining 20% - 40% of the charge time to recharge completely.
9. The process of charging a battery can reasonably be considered complete when:
   • The voltage does not continue to rise and remains stable over a measured period (voltage wins over time) or,
   • When a 100AH battery with a 3% self-discharge rate can be considered to be fully charged when the charge rate has been maintained at a level of </=3 amps for a period not longer than 4 hours (time wins over-voltage)

WARNING – DO NOT EQUALIZE CHARGE GELL OR AGM BATTERIES! Equalizing is an “over voltage-over charge” performed on flooded lead-acid batteries after they have been fully charged to help eliminate acid stratification. It helps to eliminate the acid stratification and sulfation that happens in all flooded lead acid batteries. Acid Stratification is the #1 killer of flooded lead acid batteries.

Laboratory-designed, specific to Discover, “Balance” charge algorithms have been designed and are included in all Discover recommended Industrial Commercial charges offered for sale wherever our Discover AGM and GELL VRLA DRY CELL products are sold. Visually the Balance Charging curve diagram is similar to a flooded equalize charge curve in its finishing voltage. Still, it is strictly controlled to promote proper active material conversion and not to promote gassing or bubbling of the acid to help reduce acid stratification, as in a flooded battery. Discover^’s Balance charging algorithms are HIGHLY recommended for batteries being installed in strings, larger batteries using taller plate groups and/or with batteries constantly being subjected to high-rate deep discharges.

Charging batteries properly requires administering the right current at the correct voltage. The original instructions for your charging equipment should be referenced for proper charging. Here is a list of helpful items to remember when charging.

1. Become familiar with and follow the instructions issued by the charger
2. Batteries should be charged after each period of
3. Lead-acid batteries do not develop a memory and do not need to be fully discharged before
4. Charge flooded batteries only in well-ventilated areas. Keep sparks away from charging or recently charged 
5. Verify charger voltage settings are correct for the type of battery you are charging (Flooded, AGM or GEL).
6. Correct the charging voltage to compensate for temperatures above and below25°C/77°F.

Compensation for battery temperature above or below 25°C/77°F

• Subtracting 005 volts per cell for each 1°C (0.003 volts per 1°F) above 25°C or,
• adding 0.005 volts per cell for each 1°C (0.003 volts per 1°F) below 25°C 

7. Check the water level on flooded batteries before and after charging (see the Watering section).
8. Tighten all vent caps on flooded batteries before
9. Prevent overcharging the batteries. Overcharging causes excessive gassing (water breakdown), heat buildup, and battery aging in flooded batteries and will dry out the electrolyte and damage VRLA DRY CELLAGM and GELL 
10. Prevent undercharging the batteries. Undercharging causes acid stratification in wet flooded batteries.
11. Please do not charge a frozen battery; allow it to thaw at room temperature.
12. Avoid charging at temperatures above50°C/125°F if possible.