Lawnmower batteries are not used constantly during the entire year so they need to be stored over winter while not in use. Cold temperatures can affect the acid in the battery when it is dormant. To avoid damage to the battery, and ensure longer use before replacement, the battery needs proper preparation and care for the winter months; this is especially true for areas where the temperature can fall to single digits.
Prepare the battery for winter storage by removing the battery from the mower and cleaning it before storage. Clean the terminals of any debris or corrosion to avoid damage to the terminals. Terminals can freeze because they are metal. Do not allow the battery to remain completely drained over the winter. Areas where hard or cold winters occur have near constant freezing points daily. Batteries that have no charge have a lower tolerance to freezing; this can cause the battery acid to freeze which permanently damages the battery. Partially charge the battery before storing over winter.
Batteries discharge over time during cold weather when not in use. Store the battery keeping the charge above 50 percent. If the battery charge falls below half, it should be recharged up to 75 percent to allow compensation as it discharges again. Check the battery occasionally to ensure that the charge level is being maintained.
Battery acid has a freezing point because of chemical reaction. Freezing points are determined by the charge remaining in the battery. The lower the charge, the higher the freezing point; this is also true of the reverse (low freezing point due to high charge). Because of this fact, a battery with no charge has a very high chance of freezing causing damage to the battery core. If the battery holds a charge, and is charged, it can be stored in a dry location below freezing temperatures.
Store the battery in a safe, dry location. A garage connected to a home or heated building is a good choice because the interior temperature will likely never fall below 32 degrees. Most garage interiors aren't exposed to extreme temperatures because they are enclosed. If the garage is open to elements, the battery should be stored in another location such as a basement. Basements retain radiant heat via the ground surrounding them and from the building above them.
Keeping the battery maintained over winter increases the chance of use during mowing season. Keep the terminals clean by wrapping them in plastic; this saves having to clean them during winter. Once winter is over, fill the water levels to maintain the proper acidity. Charge the battery to full power and then connect it to the mower. Turn the mower engine over once to make sure the battery works.