The frequency of corrective equalizations will vary by system due to factors such as operating temperature, frequency of cycling and depth of discharge. Loss of capacity, imbalance and low specific gravity readings are indicators.

Running frequent equalizations on batteries that do not require balancing or desulfation will overcharge and deteriorate the cells prematurely, shortening the life of the battery. We recommend performing corrective equalizations only as necessary to prevent unnecessary deterioration of oxide past in balanced, healthy cells. Note that flip-top R-Caps should be opened and vent caps, hydrocaps and watering systems should be removed during these procedures to prevent any possible buildup of hydrogen in the case.

Some systems offer a scheduled or automatic preventative equalization. These may be scheduled to run for 1-2 hours to balance and remove any buildup of sulfation that has accumulated between corrective equalizations. 

Equalization - Corrective

Corrective Equalizations should be performed when the battery bank is at 100% SOC. Review and complete the provided preparations before initiating the Equalization charge.

Equalization time will vary depending on the level of sulfation, balance of charge, size of the battery bank and available charging source. Typically, a corrective Equalization is necessary every 60 to 180 days to desulfate and balance a battery bank in systems  which are deficit cycled and/or charged at lower charge currents. If multiple parallel strings show charge imbalance it may be necessary to equalize each string individually.

It is important to monitor specific gravity and voltage throughout the Equalization process. When specific gravity readings remain constant for 45-60 minutes this generally indicates completion.


- Required Equipment: protective goggles, rubber gloves & rubber boots, hydrometer or refractometer, voltmeter, distilled water, baking soda or soda ash for possible overflow or spills

- Standard 1/4-turn bayonet caps and Rolls R-Cap flip-top recombination caps may be left on during this procedure. Dirty or clogged caps may prevent the release of hydrogen gas. Inspect and clean caps as necessary. Hydrocaps must be removed.

- Check each cell for low electrolyte levels and/or exposed plates and top up with distilled water as necessary. If the cells require watering, do so before starting the Equalization process to allow sufficient mixing with the existing electrolyte. Be careful not to overfill as the electrolyte will bubble and may overflow during the process.

- Program the Equalization voltage as recommended in Rolls Flooded Charging Parameters starting at the lower end of the voltage range for newer models.

Note: Series 4000, 4500 & 5000 models are shipped with electrolyte reaching 1.265 specific gravity at full charge. Rolls FS models are shipped with electrolyte reaching 1.280 at full charge. This is noted on the battery label.


1. Complete a Bulk & Absorption charge to bring the battery bank to 100% SOC before starting a corrective Equalization.

2. Measure the temperature of a test cell and record the specific gravity of each cell in the battery bank. Identify cells with high/low readings.

3. Initiate the Equalization charge mode at a steady low DC current (5-10% of C/20 battery capacity). If grid power is not available, use a DC power source (generator) or PV array with sufficient current when possible.

4. Specific gravity will rise across the battery bank, ideally reaching 1.265-1.270 (Series 4000/4500/5000) or 1.280-1.285 (FS models) in each cell upon completion. Readings in some cells may be slightly elevated due to electrolyte temperature (+0.05) and will return to normal when cooled but should not exceed 1.30. If the cell temperature rises above 46ºC (115ºF) and approaches 52ºC (125ºF), terminate the Equalization process and allow the batteries to cool. If available, check individual cell temperatures using an IR temp sensor to isolate any possible damaged cells.

5. If cells are severely sulfated it may take several hours for the specific gravity to rise and/or balance. If the readings plateau for 45-60 minutes, but do not reach the ideal range 1.265-1.270 (Series 4000/4500/5000) or 1.280-1.285 (FS models), stop the process to prevent cell damage and allow the batteries to cycle normally for 2-4 weeks before repeating. The cells will continue to desulfate following an Equalization as sulfate dissolves during normal charging.

Allow the battery bank to cool for 1-2 hours. Check and record the specific gravity of each cell. The gravities should be 1.265-1.270 (Series 4000/4500/5000) or 1.280-1.285 (FS models) or lower. Check electrolyte levels and add distilled water as necessary.

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, longer absorption times and/or higher voltage setting should be used. 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 small adjustments as necessary.