Equalization - Corrective

Corrective equalization needs to be performed if symptoms arise such as a constantly running generator (low capacity) or the battery bank will “not hold a charge”. These symptoms are typical of a heavily sulfated battery. If a battery is not being fully charged on a regular basis or limited equalization is performed using a generator sulfation will occur from “deficit” cycling. This undercharge condition can take months before it becomes a major and noticeable problem. This under charge condition is caused when batteries are deficit cycled. The bank receives less of a charge each cycle and starts to sulfate. Eventually the sulfate will cause a resistance to charge and a “false high voltage” reading will occur. The “false high voltage” is measured by the charge controller, which further lowers the charging current to maintain the voltage set point. This further increases the undercharge condition. This is one reason why specific gravity measurements are so important as “false high voltage” readings can be misleading.

Voltage, SG and State of Charge for information on how to correctly interpret voltage readings.

Amperage hour meters can compound the problem and cause people to believe they are returning the correct amount of energy back into the batteries to maintain a good state of charge. Amp-hr meters should be thought of as simply a fuel gauge that does not measure state of charge directly but indirectly. The state of charge is determined by using an equation (peukert's equation). Sometimes there can be fundamental errors with factors used in these calculations. You should always confirm, at least initially, state of charge by taking a specific gravity measurement of one cell when it is thought the bank is fully charged.


Corrective Equalization - Method

Corrective Equalization can take a very long time depending on the degree of sulfation. It is not recommended to equalize with a generator as some generators produce low grade AC that is not properly filtered by the inverter. This is especially true at higher voltages.


1. Recombination caps (Hydrocaps) should be removed during the equalization process to allow increased hydrogen gas to escape.
Flip-top caps (Rolls R-caps) may be left on and open.

2. Equalization voltage should be set to the recommended parameter based on system voltage. See Flooded Charging Parameters.

3. Charge at a low DC current (5-10% of C20 battery capacity). If grid power is not available, use solar panels or a DC source with sufficient current when possible. At high voltages, charging with a generator may be difficult and hard on the inverter.

4.Measure and record the specific gravity of each cell in the battery bank and temperature of a test cell. If the temperature rises above 46ºC (115ºF) and approaches 52ºC (125ºF), terminate the equalization cycle. You may need to give the batteries a chance to cool off and attempt the cycle again. Check individual cell temperatures using an IR temp sensor to isolate possible damaged cells.

5.If cells are severely sulfated, it may take several hours for the specific gravity to rise.

6. Once the specific gravity begins to rise, the bank voltage will most likely drop, or the charging current will increase. The charging current may need to be lowered if temperature approaches 46ºC (115ºF). If the charge controller has been bypassed, it should now be used or put back in line.

7.Continue to measure specific gravity until 1.265 is reached.

8. Charge the battery bank for another 2 to 3 hours, adding distilled water as required to maintain the electrolyte above the plates.

9. Allow bank to cool - check and record the specific gravity of each cell. The gravities should be 1.265 ± 0.005 or lower. Check the cell electrolyte levels and add water if necessary.


To avoid this situation it is recommended that a specific gravity reading of one pilot cell is measured and recorded on a regular basis when it is thought that the bank is fully charged. The measurement should be compared to previous readings. If the measurement is lower than the previous reading a longer absorption time and higher voltage setting should be used. Note as stated above, the longer the absorption time and the higher the bulk voltage, the more water will be consumed but less equalization will be required. Note: the specific gravity should rise as the cells use water. Look for trends in the specific gravity over a period of time and make very small adjustments as necessary.