For bigger riding mowers, the days of the old pull-cord recoil starter are pretty much over. Most larger riding mowers now feature a battery for starting, as well as a rudimentary alternator and voltage regulator as a charging system to keep the battery recharged.
While lawn mower batteries have obvious differences compared to your car's battery, there are a lot of similarities as well:
- Like an automotive battery, most lawn mower batteries utilize cells with lead plates submerged in an acid electrolyte.
- As a mower battery discharges, the plates become covered with sulfate and the acid becomes alkaline. As it charges again, the sulfate in the plates goes back into the acid electrolyte and turns it acidic.
- As with an automotive battery, the acid content and antimony in the mower's battery can cause corrosion problems.
- Most lawn mower electrical systems are designed to operate from a 12v battery.
The lead-acid battery design is over 100 years old now, and it comes with problems. It's hazardous to handle and dispose of, and the batteries aren't as well insulated from the constant vibration of a mower's engine as a battery in a car's engine compartment would be. Some mower batteries now feature an absorbed glass mat or gel cell design, which limit the amount of liquid in the battery for safer handling. AGM and gel cell batteries do come at a premium price, however.
How Are Mower Batteries Rated?
Like with an automotive battery, a mower battery is rated on cold cranking amps (CCA). A CCA rating is a measure of how much current the battery can deliver for 30 seconds at 0 degrees Fahrenheit. It's probably not too likely that you'll be running your mower in zero-degree weather (unless it's a snow blower), but the CCA will give you a good indication of how robust the battery is and what you can expect.
Mower batteries are also rated by their physical size, according to standards from the Battery Council International. Most mower batteries are Group U1, which means they're 8.3 inches long, 5.1 inches wide, and 7.25 inches high. The dimensions are important, as the battery has to sit in the tray and the engine compartment properly, and must be able to connect to the battery cables.
When you're shopping for a mower battery, you do get what you pay for (just like with an automotive battery), and make sure to match the terminals and make sure the replacement battery has at least as many CCAs as the original. And if you want to save time and money, one way to extend the life of lawn mower batteries is to leave them on a battery maintainer over the winter.