Winter Battery Storage
By: US Battery
Flooded lead-acid batteries will charge and discharge at different rates depending on the temperature. In winter, the colder temperatures bring additional risks of damage if the batteries are not stored properly. U.S. Battery’s Senior Vice President/Engineering, Fred Wehmeyer, offers some tips to working with and storing batteries in cold temperatures.
Never Store Discharged Batteries
One of the most common mistakes is leaving FLA (Flood Lead Acid) batteries stored in a discharged state. Storing a discharged battery in extremely cold temperatures can allow the electrolyte to freeze, causing it to expand and in doing so 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.
One of the most common mistakes is leaving FLA (Flood Lead Acid) batteries stored in a discharged state. Storing a discharged battery in extremely cold temperatures can allow the electrolyte to freeze, causing it to expand and in doing so 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.
How To Prepare Batteries For Winter Storage
For areas where freezing temperatures are normal, it’s important to properly prepare the
batteries for storage. First, check the battery’s state of charge by taking specific gravity readings with a hydrometer. Temperature affects these readings, so it’s important to add a correction factor that varies with the electrolyte 
temperature. 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 0.012. 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. 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 0.012. 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.
Cold Affects Charge and Discharge Rates
In areas where temperatures are not so extreme (freezing) and 
batteries will still be functioning on any vehicle or equipment, it’s important to remember that the colder temperatures will also affect the charge and discharge rates. Batteries will charge and discharge more slowly in cold conditions and will also exhibit lower capacity. Cold temperatures slow down the reactions in the battery’s chemistry and result in a reduction in battery capacity. A general rule of thumb for this effect is for every 15-20 degrees below 80°F, the battery loses 10 percent of its capacity.
batteries will still be functioning on any vehicle or equipment, it’s important to remember that the colder temperatures will also affect the charge and discharge rates. Batteries will charge and discharge more slowly in cold conditions and will also exhibit lower capacity. Cold temperatures slow down the reactions in the battery’s chemistry and result in a reduction in battery capacity. A general rule of thumb for this effect is for every 15-20 degrees below 80°F, the battery loses 10 percent of its capacity.