Luckily for homeowners, replacing a lawn mower battery is a fairly easy and straightforward process. Lawnmower batteries typically have a long lifespan, with a replacement being necessary about every two to four years over the life of your mower. If you're having trouble starting your lawnmower and suspect that the source of trouble is the battery, try recharging the battery first before actively seeking a replacement. In particular, a recharge should definitely be attempted if the battery is less than two years old. If your lawnmower battery does not respond to multiple recharge attempts, you can consider it officially dead and begin looking for a new one in earnest.
Make sure when shopping for a new lawnmower battery that you bring information regarding the brand, model number and year of your lawn mower, as well as the voltage of the battery. A smart alternative is to bring the old battery itself along with you. This makes it easier for customer service personnel to determine exactly what replacement battery you'll need quickly and accurately. It also gives you the opportunity to hand the battery over to the store for proper recycling or disposal if they have a program for this purpose. Remember: it is illegal to dispose of old lawnmower batteries by simply throwing them in the trash!
Before attempting to replace the battery in a riding lawnmower, make certain that the ignition key is in the "off" position. Both riding and push lawnmowers should be completely disengaged and parked on a level surface in a well-lit area. If you're replacing the battery of a riding lawnmower, access the battery by tilting the seat back or by lifting the hood. Push lawnmower batteries can be accessed by temporarily removing the deck of the mower.
Loosen the straps which are holding your battery in place if you're working with a riding lawnmower. Wearing gloves is strongly recommended at this point to avoid mild-to-severe skin irritation, since your old lawnmower battery may have lead acid residue on its outside container. Using an adjustable wrench, loosen the nuts which are keeping the ends of both the black and red cables clamped onto the terminals of the old battery. Examine how the old battery is positioned on its tray before lifting it out so that you'll know how to properly position the new one. Pushing the loosened cables off to the side, use your wrench to loosen and remove the brace or clamp which is holding the battery in place on its tray. Lift the old battery out and place it off to the side and out of the way.
For the terminals of your new battery to work effectively, they will have to have a clean connection to the battery cable ends. To ensure a clean connection before securing the cable ends onto the new battery, you'll need to thoroughly scrub these ends to remove any greasy residue or rust buildup due to corrosion. Make a thick, mushy paste of baking soda and water in a paper cup or small disposable plastic container. Dip the end of a small wire brush into the paste and scrape the rounded insides of the cable ends in an aggressive circular movement by twisting your wrist. Use the paste and the wire bristles to vigorously abrade these cable ends so that they're clean and smooth to the touch. Periodically wipe the insides of the cable ends off with a cloth rag to see how much buildup you've managed to remove. You'll want these ends to be as clean as possible for maximum performance from your new battery.
Put your replacement battery on the tray in the same position as the old battery was placed. Push the end of the red cable down on the positive terminal of the new battery, and the end of the black cable down on the negative battery terminal. Secure the nuts of the cable ends firmly onto their respective terminals with your adjustable wrench. If you're replacing a riding lawnmower battery, tightly secure the straps you loosened upon removal, and lower the seat or lawnmower hood back down. Push lawnmowers can now have their decks put secured firmly back in place. Lastly, as a way of extending the life of your new battery a little further, remove the battery in the fall and store it in a safe place which is cool and dry until the spring.