Whenever you install a battery, your primary concern should be safety. Before installing your battery, make sure that your riding mower is parked in an open area. Batteries can emit a toxic gas that can be harmful in an enclosed space. Also ensure that all electrical devices are switched to the "off" position. Once the safety concerns are in place, installing a riding lawn mower battery is not much different than installing one in a car.
Check your riding lawn mower's manual. It may include model-specific instructions concerning lawn mower battery installation. If you have misplaced the manual, search for a copy online by entering the name, model, make and "manual" into a search engine. Or, call the manufacturer to order one.
Check the battery cables. Look for any cracks or signs of corrosion. If the battery cables are damaged, they will need to be replaced before you install the battery. If they are in good condition, use a toothbrush dipped in equal parts baking soda and water to clean the connectors.
Place the lawn mower battery in the metal housing case or tray. In most models, this is located underneath the hood, near the engine. When placing the battery in the case, make sure that the positive terminal is on the same side as the positive battery cable.
Attach the battery to the cables. Attach the positive cable (red or marked by a "+") to the positive terminal on the battery. Then tighten the clamp by screwing it tight with your hands or a pair of needle-nose pliers. Then attach the negative cable (black or marked by a "-") the same way.
Secure the battery in the housing. Some models of riding lawn mower's come with a battery cover. Others have a strap that will need to be secured. And still other models come with a metal bar that may need to be screwed or bolted on.