Preventive Maintenance, Charging and Equalization

Bulletin # 5


Please do not perform any of the tasks listed below, until you have completely read Bulletin #7 on Battery Safety.

This bulletin describes preventive maintenance and recommended charging procedures to maximize battery life. The leading cause of premature battery failure is improper charging and poor battery maintenance.

Equalization is very important and must be preformed correctly but only as required.

Preventive Maintenance                                                         

When a battery is first received the cell acid levels should be checked and the battery should be put on charge. After removing from charge the specific gravity readings of each cell should be recorded and kept for the life of the battery.

Preventive maintenance involves, at a minimum, checking the cell electrolyte level for correct acid volume once a month and equalizing once every six months. The cells should be watered back to the original acid level which is ¼ - ½" below the bottom of the vent well (tube inside the battery cell with slots on each side). Distilled water is preferred but local water (not chlorinated) maybe acceptable if it is not "hard" or does not contain high iron levels.

A recommended preventive maintenance program can be summarized as follows:

Occasionally cleaning the battery terminals and case / cover is a good practice and recommended. A weak solution of household baking soda and water can be used to neutralize any spilled acid (100 g per liter or 4 Oz per pint). Make sure the vent caps are securely tightened and NO soda solution gets into the battery cells.

Good record keeping is stressed as review of these records can help to determine the "health" of the battery and can prove invaluable if system problems develop.


State of Charge and Charging                                               

The truest measure of a battery's state of charge is the SPECIFIC GRAVITY of the battery acid. The following shows the approximate state of charge at various specific gravities at 77ºF / 25ºC.

Charged Specific Gravity
100% 1.265-1.275
75% 1.225-1.235
50% 1.190-1.200
25% 1.155-1.165
0% 1.120-1.130

Hydrometers can be difficult to use and at best accurate to +/-0.005 points.

Please see Bulletin # 6 for correct hydrometer use.

We recommend a three step charging procedure. Recommended voltage settings are as follows:

Volts per cell
2.58 -2.67 (max)
2.37-2.45 (max)
2.20-2.23 (max)

To calculate the correct settings for another battery bank voltage divide the total nominal voltage by two and use this number as a multiplier. For example a 18V system, 18/ 2 = 9, equalization preferred = 9 x 2.58 = 23.2 V

Caution: The ideal float voltage is the lowest voltage setting that will maintain the battery at full charge. The higher the voltage the more water the cell will consume. The minimum equalization voltage is highly recommended unless it is suspected a sulphation problem exists.


Equalization is required to mix the battery acid and bring every battery plate to an equal charge. Equalization should only be performed when required or once every six months. Equalization is required when the cell specific gravities vary from highest to lowest by +/- 0.015 (1.245 - 1.260 at full charge). The exact particulars (such as charging time and currents) are dependent on the charging system. However, the point is to bring the batteries up to the equalization voltage and continue charging for 1-2 hours at a low current, without excessive heat. The final or finishing charging current should be 3-7% (we recommend 5%) of the 20 hr capacity in amps. If battery temperature exceeds 125ºF the battery should be taken off of charge and allowed to cool before equalization is continued. When two consistent specific gravity readings are taken a half hour apart the battery is equalized. It is recommended to water the battery cells before or half way through the equalization. This is to assure the water is completely mixed into the electrolyte.

Caution: If you have HYDROCAPS, remove during equalization.

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