Flooded lead-acid batteries used in a variety of applications have charge and discharge rates that depend highly upon temperature. While warmer climates tend to speed-up charging and discharging rates, cold winter months can slow down the rate of charge/discharge. In addition to affecting rates, colder temperatures also carry the risk of freezing the electrolyte if the battery is not stored properly.
One of the most common mistakes during winter months is storing flooded lead-acid batteries in a discharged state. A discharged battery in extremely cold temperatures will allow the electrolyte to freeze, causing it to expand. Electrolyte expansion can crack the battery case, causing a leak or complete battery failure. A fully charged battery has a freezing point around -80 °F while a discharged battery has a freezing point around 20 °F. By keeping the battery fully charged during the winter months, the electrolyte is less likely to freeze and cause unexpected failures.
With that said, don’t expect to charge your batteries and come back in the spring expecting everything to be okay. In cases where complete vehicle fleets are stored away during the winter, it is important to consistently check the battery’s state of charge by taking specific gravity readings. Like charging rates, temperature also affects your readings, so it’s important to add a correction factor that varies with the electrolyte temperature. The optimum temperature to take a hydrometer reading is 80 °F (27 °C). As a rule of thumb, subtract four points (.004) from your hydrometer reading for every 10-degrees below 80 °F (5.6-degrees below 27 °C). For example; if the temperature of the electrolyte is 50 °F and your battery specific gravity reading is 1.200, you must subtract .012 from your reading. In this case .004 for every 10-degrees equals .012. Subtract this from 1.200 and your corrected specific gravity reading is 1.188. In this example, the battery cell is less than 50 percent charged and should be recharged before being put into winter storage; (a fully charged battery should read approximately 1.270). If your corrected specific gravity readings are low, fully charging the batteries will put them in a safe state for storage.
Temperature also effects charge and discharge rates. A cold battery will charge and self-discharge slower than a warm battery, but will also exhibit lower capacity. This is especially true for battery powered fleets that are that are able to operate in colder temperatures during winter months. Although these fleets may not experience freezing temperatures, the cold temperature increases the resistance in the battery’s chemistry and causes a reduction in battery capacity. A general rule of thumb for capacity is for every 15-20 degrees below 80 °F, the battery loses 10 percent of its capacity.
The ability to check specific gravity readings in flooded lead-acid batteries is an advantage in cold weather operation. It allows the operator to fully understand the effects of cold temperature on the batteries, and allows them to be properly maintained. While the downside of storing or operating golf car batteries in the winter requires regular specific gravity checks, one positive aspect is that colder temperatures also reduce self-discharge rates. In the long run, taking the time to check the state of charge on your fleet’s batteries will ultimately be more cost effective than having to replace one or more damaged batteries. To find additional resources on battery maintenance and ways to increase battery efficiency and service life, visit U.S. Battery’s website at www.usbattery.com.
By Fred Wehmeyer, Senior Vice President/Engineering U.S. Battery Manufacturing[/vc_column_text][/vc_column][/vc_row]