When working with batteries and their electrolyte, be sure to put on goggles and chemical-rated gloves, but first remove all jewelry and/or watches, which could accidentally come into contact with battery terminals and cause arcing. A good flashlight is usually needed to see the level of the electrolyte inside of the battery—but be sure its housing is not metal, either.
The electrolyte on a properly filled battery should be approximately 1/4 inch below the fill tube. If the battery is overfilled, the electrolyte can flow out of the vent caps when the battery is charged, as bubbles of hydrogen and oxygen that are produced cause the electrolyte’s level to increase.
Sometimes, battery cables or other obstructions can make maintenance of one particular cell, battery, or even an entire battery string, difficult. Pay attention to these types of problems and correct them, as seemingly small improvements can have a dramatic effect on the frequency of future maintenance and battery longevity.
While a voltage measurement provides a quick side-by-side comparison (identifying potentially weak batteries or cells), the overall battery voltage fluctuates significantly depending on if the battery is being charged, discharged, or if it has been at rest. For flooded batteries, specific gravity (SG) readings show the actual concentration of sulfuric acid in the electrolyte and thus are a much better indicator of the battery’s state of charge (SOC) for each cell and the entire battery. SG can only be measured on nonsealed, flooded-type batteries.
Measure and record each cell’s SG with a hydrometer or refractometer, using all the same protective equipment as you’ve used for checking the electrolyte levels (see “Methods” in this issue). To correlate an SG value to the SOC level, check the SG graph or table from the battery manufacturer’s specifications. For example, a typical SG reading for a battery at 100% SOC is 1.265. If the difference in SG between any two cells is greater than 0.025, the battery bank needs to be equalized to ensure that all cells receive a full charge.
Battery capacity and cycle life are typically provided for a battery at a temperature of 77°F (25°C). If the battery is colder or warmer, the specification and performance will vary. At lower temperatures, the battery’s available capacity (measured in amp-hours) will be decreased. At higher temperatures, the battery’s life (number of cycles) will be diminished.
The “Typical Life Cycles vs. Average Depth of Discharge” graph shows the number of charge/discharge cycles versus the depth of discharge (DOD) for a typical flooded lead-acid (FLA) battery at 77°F and 95°F. Most FLA batteries will be able to supply only half as many cycles when the battery temperature is increased by 10°C (18°F). For example, at 25°C (77°F), a battery may be rated at 2,000 cycles at a 20% DOD. But when operated at the higher temperature of 35°C (95°F), it will only provide 1,000 cycles under the same cycling conditions.
Factors like lack of ventilation, heat or sunlight exposure, and high charging voltages and currents can also increase a battery’s internal temperature. Operation at consistently high internal temperatures can significantly reduce a battery’s life.