Battery Maintenance

The advice on this page is intended as general guidance only. Always consult your battery manufacturers documentation and follow the manufacturer’s recommendations for maintenance, testing and charging.

For more information on batteries including how to select see our main battery page

This page contains information on

• battery maintenance
• battery testing procedure
• multi stage battery charging.

Information on Battery State of Charge vs. Voltage can also be found here >>>

Battery Maintenance

Batteries should ideally be inspected at least once a month to check for:

Water level. Water should be added when the level drops about 15mm (1/2 ") below the full level.

	Add only approved water to the cells. Distilled water is recommended. Water with a high mineral content must not be used.
	Add water to batteries after charging to prevent overflow of acid due to expansion. Fill all cells to the proper level.
	Do not overfill cells. Fill to within 1/8" of level indicator or 1"-2" over the top of the separators.
	Do not use a hose to water batteries.
	Spot check cells between waterings to assure electrolyte is above separators. Excess water usage indicates the presence of any or all of the following conditions: a. Overcharging. b. High temperature operations. c. Nearing end of service life.
	Do not allow the electrolyte level to drop below the top of the separators since this will lead to shortened battery life.

SAFETY NOTE

Batteries contain acid which can be harmful if splashed on your skin or in your eyes. Accidents happen when acid gets on hands and is then accidentally rubbed into eyes. When dealing with batteries always wear safety goggles and ensure a good supply of clean water is handy to wash hands or rinse eyes if needed.

Clean batteries after watering or when washing equipment.

	Wash the tops of the batteries making sure the vent caps are in place. Do not allow water or other foreign matter to enter the cells.
	Use a solution of bicarbonate of soda, one cup for each bucket of water, to wash batteries if there is an accumulation of acid residue.

When watering batteries inspect battery and other terminal connection for:

	Corrosion; Clean connections with soda solution, and wire brush and apply a non-metallic grease or protective spray to retard further corrosion.
	Loose Connectors; Be sure all connections are tight and that there is good contact with terminals. Loose connectors can also cause explosions and serious injury.
	Broken or Frayed Cables; Replace any which look suspicious.

SAFETY NOTE

When using any metal tools to maintain batteries ensure the handles are well insulated to reduce the risk of shorting any battery terminal.

Spot check battery specific gravity

Once a month, spot check two or more cells for specific gravity reading. Gravity should be 1.220-1.280. See table 1. If low readings are noted:

	Check charger to insure that proper charge is being returned to the batteries.
	Check connections as specified (See Inspection above).
	Check all cells to determine if batteries are near the end of life.

The following tables are presented as guidance only, for exact information on the relationship between specific gravity/voltage and the state of charge of your battery, consult the battery manufacturer's own specification.

Table 1. Specific gravity and its relationship to state of charge

Specific Gravity	% of Full Charge
1.280	100%
1.250	80%
1.220	60%
1.200	40%
1.170	20%
1.140	0%

Table 2: Voltage and its relationship to state of charge

Voltage	% of Full Charge
12.7	100%
12.5	80%
12.3	60%
12.1	40%
11.9	20%

Battery Testing Procedure

When equipment operates less than its normal specified running time, the batteries should be examined as follows:

	Check terminal connections for corrosion, loose connections and broken or frayed cables.
	If terminal connections appear to be in good condition, check all cells with a hydrometer for variation in specific gravity. When there are variations of 30 points or more, mark low cells. This may mean an aging or defective battery.
	Recharge the batteries as recommended by the manufacturer.
	Read all gravities again after recharge. Batteries are serviceable at gravities of 1.250 to 1.280. If one cell in a battery varies by 30 points or more than another cell in the same battery, it is an indication of a bad cell, assuming no acid has been spilled or pumped from cells with low specific gravity.

Multi-Stage Battery Charging

A typical 12-volt lead-acid battery must be taken to approximately 14.2-14.6 VDC before it is fully charged. (For 24 volt systems double these figures for 48 volt, multiply by four.) If taken to a lesser voltage level, some of the sulfate deposits that form during discharge will remain on the battery's lead plates. Over time, these deposits will cause a 200 amp-hour battery to act more like a 100 amp-hour battery, and battery life will be shortened considerably. Once fully charged, batteries should be held at a lower float voltage to maintain their charge - typically 13.2 to 13.4 volts. Higher voltage levels will "gas" the battery and boil off electrolyte, requiring more frequent maintenance.

Most automotive battery charger designs cannot deal with the conflicting voltage requirements of the initial "bulk charge" and subsequent "float" or maintenance stage. These designs can accommodate only one charge voltage, and therefore must use a compromise setting - typically 13.8 volts. The result is a slow incomplete charge, sulfate deposit build-up, excessive gassing and reduced battery life.

More anvanced invereter / chargers such as the Xantrex, automatically cycle batteries through a proper three stage sequence (bulk, absorption and float) to assure a rapid and complete charge without excessive gassing.

Factory battery charger settings on most inverter-charger combinations are optimal for a lead acid (liquid electrolyte) battery bank of 250-300 amp hours in a 70°F environment. If your installation varies from these conditions, you will obtain better performance from your batteries if you adjust the control settings.

The Maximum Charge Rate in amps should be set to 20-25% of the total amp-hour rating of a liquid electrolyte battery bank. For example, a 400 amp-hour bank should be charged at no more than an 80 -100 amp rate. Excessive charge rates can damage batteries and create a safety hazard.

The Bulk Charge Voltage of typical liquid electrolyte lead acid batteries should be about 14.6 VDC. There is no one correct voltage for all types of batteries. Incorrect voltages will limit battery performance and useful life. Check the battery manufacturer's recommendations.

The Float Voltage setting should hold the batteries at a level high enough to maintain a full charge, but not so high as to cause excessive "gassing" which will "boil off" electrolyte. For a 12-volt liquid electrolyte battery at rest, a float voltage of 13.2-13.4 is normally appropriate; gel cells are typically maintained between 13.5 and 13.8. If the batteries are being used while in the float stage, slightly higher settings may be required.

Charge voltage guidelines used here are based on ambient temperatures of 70°F. If your batteries are not in a 70°F environment, the guidelines are not valid. Temperature Compensation automatically adjusts the voltage settings to compensate for the differences between ambient temperature and the 70°F baseline. Temperature compensation is important for all battery types, but particularly gel cell, valve-regulated types which are more sensitive to temperature.