Lawn mower batteries can lose the electrical charge when the machine is stored over winter. This does not necessarily mean that the battery needs replacing. In most cases, a thorough charging from a battery charger will bring the electrical storage device back to life. Pay attention to the individual voltage of the lawn mower battery. Most starting batteries are in the 12-volt range, while some are the 6-volt type. Be sure the battery charger is rated to handle the correct charging voltage for your particular battery.
Gain access to the battery compartment on your model of lawn mower. Various manufacturers will have different locations for the battery. Consult the manufacturer's specifications for these locations.
Use the correct size end wrench to remove the battery cable connectors from the battery terminals. The most common wrench size for battery clamps is a 7/16-inch wrench. Loosen the negative (-) cable clamp first. Remove the connector and set it to the side. Loosen and remove the positive (+) cable clamp. Set the cable to the side.
Remove the battery from the lawn mower. Set the battery on a firm, level surface in a well-ventilated area.
Attach the red clamp connector from the charger to the positive (+) terminal on the battery. Secure the black clamp connector from the charger to the negative (-) terminal on the battery.
Turn the charger to the correct voltage level, if applicable, on the face of the charger unit. Plug the battery charger into a wall electrical outlet. Turn the charger to the "on" position.
Allow the battery to fully charge. Most battery chargers will have a meter on the face of the charger. This meter is generally labeled as "amperes." The battery will be fully charged when the meter shows a "0 amperes" reading. Some chargers may also have a green light that signifies a full charge to the battery. Various charger models will have different identification methods. Consult the charger manufacturer's labeling for the correct instructions.
Replace the battery into the lawn mower using the reverse instructions as described above.