Most batteries found in riding lawn mowers are 12-volt. This standard voltage applies to mowers using a traditional internal combustion engine, where the battery is required only to start the machine. The 12-volt power supports the entire electrical system, including the starter motor, ignition, and any onboard lights. This nominal 12-volt rating is an established industry standard for small engine equipment, balancing power delivery and component safety.
The Standard Voltage for Starting Engines
The 12-volt standard for gas-powered riding mowers relates directly to the demands of starting a small engine. To turn the engine over, the battery must deliver a sudden surge of electricity to the starter motor. This initial current is quantified by the Cold Cranking Amps (CCA) rating, which measures the battery’s ability to deliver current at a low temperature.
The 12-volt system is achieved by connecting six separate 2-volt lead-acid cells in a series within the battery casing. This configuration provides the electrical pressure necessary to overcome the engine’s compression during starting. A fully charged 12-volt lead-acid battery registers a static resting voltage between 12.6 and 12.8 volts. The 12-volt designation is practical because it allows for a high current draw without requiring excessively thick wiring or complex safety measures.
Battery Types and Voltage Exceptions
While 12 volts is the norm for starting batteries, exceptions exist depending on the mower’s design. Some older push mowers with electric start may use a 6-volt battery, though this is rare on modern equipment. Common 12-volt types include flooded lead-acid and Absorbed Glass Mat (AGM) batteries. Flooded batteries contain liquid electrolyte, while AGM batteries use a fiberglass mat to suspend the electrolyte, making them more resilient to vibration.
The most significant voltage exceptions are found in modern electric and cordless lawn mowers. These machines lack a combustion engine and rely on the battery pack for propulsion and blade power. These fully electric mowers use high-voltage lithium-ion packs, typically ranging from 40 volts up to 80 volts. This high voltage is necessary to drive the electric motor efficiently over a longer period, acting as a primary power source rather than just a starter.
Practical Differences from Automotive Batteries
Although both lawn mower and car batteries operate on a 12-volt system, they are not interchangeable due to key practical differences. The most immediate distinction is physical size; mower batteries are significantly smaller and designed to fit into a compact compartment, often conforming to the common U1 group size. Terminal orientation is also a factor, as the positive and negative posts must align correctly with the mower’s cables.
The most important performance difference is the Cold Cranking Amps (CCA) rating. Since lawn mower engines are much smaller than automobile engines, they require substantially less power to turn over. A typical riding mower battery may have a CCA rating between 100 and 300 amps, often only one-third of the power a standard car battery delivers. A car battery is engineered for a single, high-output burst to start a large engine, while a mower battery is tailored specifically to the lower power requirement of a small engine.