Importance Of Proper Testing To Maintain Battery Health
Edition: March/April 2012
Monitoring the overall health of your deep-cycle batteries is vital to ensuring that a golf car will make it through more than just one round of golf. Physical inspection alone, while important, is not sufficient to determine the condition of your batteries. Instead, measuring and understanding the state of charge (SOC) of a golf car’s batteries are key to maintaining their performance and extending their overall lifecycle, giving players more time on the course.
Both open-circuit voltage and specific gravity readings can give a good indication of the battery’s state of charge and health. Conducting these routine checks not only shows the state of charge, but also helps spot signs of improper care, such as undercharging and over-watering, possibly locating a bad or weak battery, or identifying a charging issue.
There are several tools and methods for measuring SOC for both flooded lead acid (FLA) and valve-regulated lead acid (VRLA). For both FLA and VRLA you can take the open-circuit voltage reading with a voltmeter. For FLA batteries measuring the specific gravity of individual flooded battery cells is another method and can be done with an inexpensive hydrometer. Measuring the specific gravity of FLA batteries is believed to be the more accurate indicator of the SOC, but must be temperature corrected and requires using a thermometer to be accurate.
Before measuring the SOC by voltage or specific gravity readings you must ensure there is no load on the batteries and they are fully charged before you begin. Also, it is important that anytime you are working around batteries you use proper personal protection equipment including safety glasses to protect your eyes and gloves to ensure no electrolyte comes in contact with your skin.
This method is the most economical process for testing either type of battery technology (FLA or VRLA), and requires using an inexpensive digital voltmeter which should have a basic accuracy at least 0.5% or better. Prior to taking voltage readings, it is important that you allow the batteries to sit for at least two hours after charging to let the voltage settle to its normal open circuit state.
To begin, set the voltmeter to the proper voltage range that corresponds with the voltage of the battery you are testing. Touch the positive lead from the voltmeter, usually red in color, to the positive terminal of the battery. Touch the negative lead, usually black in color, to the negative terminal of the battery. The voltmeter will then provide a voltage value. Be sure to note if the value is negative or positive, as you may have connected the leads in reverse, or it can indicate that the battery has a negative voltage.
Also, it’s important to know that as batteries age, the voltage reading will gradually get lower. If the batteries have not been properly maintained, this will happen more quickly.
Measuring By Specific Gravity
Measuring specific gravity is the most accurate method for testing FLA battery types and measures the density of the battery’s electrolyte. You will use a battery hydrometer that reads in the range you are measuring. A typical range would be a specific gravity of 1.000 to 1.300. Since temperature correction is required to ensure an accurate reading, you also will need a thermometer to measure the temperature of the electrolyte.
You’ll begin by siphoning out, or removing, electrolyte from the battery cells, and it is extremely important to wear goggles and rubber gloves. Also, be sure to keep baking soda and water handy to neutralize electrolyte in case of spills.
Begin by removing the vent caps on the battery. Insert the hydrometer into each cell and siphon enough electrolyte to make the graduated float inside of the hydrometer rise. To obtain an accurate reading, be sure the float is not touching the sides of the hydrometer. Record the value on the float where the electrolyte crosses it. Don’t forget to insert the thermometer into a center cell and record the temperature once it stabilizes. To correct specific gravity readings for temperature, add 0.004 for every 10°F (5°C) above 80°F (27°C) and subtract 0.004 for every 10°F (5°C) below 80°F (27°C).
Calculate the average of each of the readings and compare the result with the chart provided by the battery manufacturer to accurately determine the battery’s state of charge.
If the specific gravity values are consistently low, such as less than 1.250, it could be due to the batteries not being fully charged or the recent addition of water which dilutes the electrolyte at the top of the cell. In both of these conditions, the battery should be given a sufficient equalization charge that results in specific gravity readings that are representative of the batteries true state of charge.
Keep a Battery Maintenance Log
It is very beneficial to keep a log of both voltage and specific gravity readings over time to refer to when trouble shooting potential problems with your batteries in the future. It also reinforces a commitment to a regular battery maintenance program.
When using voltage or specific gravity readings to determine a battery’s state-of-charge, it’s important to always consult the manufacturer’s technical specifications. Not all batteries operate with the same electrolyte specific gravity, so it’s important to ensure that you are using the battery manufacturers’ correct measurement criteria.