One of the most critical functions of a riding lawn mower battery is to provide the power to start the lawn mower. Another function is to operate the many electronic controls of the lawn mower. An alternator in the lawn mower keeps the battery charged. After a period of time, though, the lawn mower battery must be replaced--it's simple to figure out what battery model you have, so you can get the correct replacement.
Look at your brand of battery. You may be able to directly replace the battery with the same make and model number. Check your local home improvement store to see if it is still sold there.
Consult your lawn mower's operation manual. The type of battery that the lawn mower uses is usually listed in the operation manual.
Go to your local home improvement store. Most of the time in the aisle that contains the battery there will be an information book that lists all the brands of lawn mowers. If you go to your specific brand and model you will be able to purchase the correct battery.
Look for your lawn mower battery information online. You can search for your lawn mower brand and model number. It will then tell you which battery is to be used in your lawn mower. See Resources for a good online battery search website.