A lawn mower battery will eventually lose its charge. When this occurs, the electrical storage device is perhaps still good and should not be thrown away as a disposable item. It is worth the effort to remove the battery from the lawn mower and connect it to a battery charger. The best type of battery charger to use is a multistage charger. The multistage battery charger will constantly monitor the amount of power that is being fed to the battery. This will help to extend the life of any battery.
Locate the battery on the lawn mower. Some models may house the battery in an enclosed plastic container. Some may be under the seat.
Use the end wrenches to remove the battery cables from the terminal posts on the battery. In most cases, either a 7/16-inch or a 1/2- inch end wrench will loosen the connection clamps on the battery posts. Remove the negative terminal first. Set the cable to one side. Disconnect and remove the positive cable from the battery last.
Pull the battery from the lawn mower. Set the battery on a firm surface, preferably outdoors.
Check the fluid level in the battery if the battery is a full service type. A full service battery will allow you to remove the top caps on the battery. Not all batteries are fully serviceable. Use the distilled water to top off the level of fluid, if applicable. The level of battery fluid must be to the bottom of the internal plastic rings in each battery cell.
Connect the battery to the charger in the following order. Attach the red clamp from the battery charger to the positive terminal post on the battery. Secure the black clamp from the charger to the negative terminal post on the battery.
Plug the charger into the wall outlet. Follow the manufacturer's instructions as to the indicator lights on the front of the battery charger. In most cases there are two LEDlights. The green LED indicates that power is going to the battery. The red LED indicates a heavy charge is being sent to the battery. If either of the two lights is blinking, this may indicate a problem. Consult the instructions as various manufacturers will use different codes for indicating a problem.