Most lawn mower batteries are 12 volts, but some are 18 volts or higher
The voltage of a lawn mower battery tells you how much electrical power it delivers to the motor. A 12-volt battery is the standard for most gas-powered mowers with electric starters and for many cordless electric mowers. Some newer cordless models use 18-volt, 20-volt, 40-volt, or even 80-volt batteries — the higher the voltage, the more power the mower can draw, which usually means faster cutting and longer runtime before the battery drains.
The voltage you need depends on the type of mower you own. If you already have a mower, the voltage is printed on the battery itself and in your owner's manual. If you are buying a replacement battery, matching the voltage exactly is essential — you cannot use an 18-volt battery in a 12-volt mower, and doing so will damage the mower's electrical system.
Key Takeaways
- Gas mowers with electric starters almost always use 12-volt batteries, while cordless electric mowers range from 12 volts to 80 volts depending on the brand and model.
- The voltage is printed directly on the battery casing and in your mower's manual, so you can identify it in seconds without guessing.
- Replacing a battery with the wrong voltage will damage your mower's motor and charging system.
- Higher-voltage batteries (40V, 80V) deliver more power and longer runtime but cost more and are heavier than lower-voltage options.
- Some manufacturers like DeWalt and Makita make batteries that work across multiple tools in their product line, so check whether your mower's battery fits other equipment you own.
12-Volt batteries in gas mowers with electric starters
If you own a gas-powered lawn mower with an electric starter button, it almost certainly has a 12-volt battery. This battery does not power the cutting blade — the gasoline engine does that. Instead, the 12-volt battery powers the starter motor, which cranks the engine to life when you press the button.
These batteries are usually small, about the size of a car battery but lighter, and they sit in a plastic holder under the mower deck or near the engine. When the engine is running, the mower's alternator recharges the battery so it is ready for the next start. If your mower is hard to start or will not start at all, a dead or weak 12-volt battery is often the culprit.
A replacement 12-volt lawn mower battery typically costs between $30 and $80, depending on the brand and whether it is original equipment or an aftermarket part. Most hardware stores and online retailers stock them, and installation usually takes less than five minutes — you disconnect the old battery's terminals and connect the new one in the same way.
18-volt and 20-volt cordless mower batteries
Cordless electric mowers in the 18-volt to 20-volt range are popular for small to medium yards. These batteries power the cutting motor directly, so the voltage determines how much cutting power the mower has. An 18-volt or 20-volt mower can handle regular lawn grass and light weeds, though it will slow down in thick or wet grass.
Brands like DeWalt, Makita, and Ryobi make 18-volt and 20-volt batteries that fit not only their mowers but also their drills, saws, and other cordless tools. If you already own tools from one of these brands, buying a mower that uses the same battery voltage means you can swap batteries between devices and only need to charge one type of battery. This can save money over time because you are not buying separate batteries for each tool.
Runtime on an 18-volt or 20-volt battery typically ranges from 30 to 60 minutes of continuous mowing, depending on the battery's amp-hour rating (how much charge it holds) and how thick your grass is. A single battery often runs out before you finish a large yard, so many people buy two batteries and rotate them — one charging while the other is in use.
40-volt and 80-volt batteries for larger cordless mowers
Higher-voltage batteries — 40 volts and 80 volts — are found in cordless mowers designed for larger yards or commercial use. A 40-volt mower can cut faster and handle thicker grass than an 18-volt model, and an 80-volt mower is powerful enough for properties an acre or larger. The trade-off is that these batteries are heavier, more expensive (often $150 to $400 per battery), and take longer to charge.
Brands like Ego, Greenworks, and Toro focus on the 40-volt and 80-volt market. Like the lower-voltage brands, they often design their batteries to work across multiple tools — an 80-volt Ego battery can power an Ego mower, string trimmer, leaf blower, and hedge trimmer. If you plan to build a collection of cordless yard tools, choosing a brand and sticking with it means all your tools share the same battery ecosystem.
A 40-volt or 80-volt battery typically delivers 45 to 90 minutes of runtime on a single charge, though this varies widely based on grass thickness, blade height, and the battery's capacity. These mowers are quieter and produce zero emissions compared to gas mowers, which appeals to people in noise-restricted areas or those who want to reduce their environmental footprint.
How to find the voltage of your current battery
The easiest way to find your battery's voltage is to look at the battery itself. The voltage is printed on a label on the side or top of the battery casing — you will see "12V", "18V", "20V", "40V", or "80V" clearly marked. If the label is worn or hard to read, open your mower's manual and look in the specifications or parts diagram section; the voltage will be listed there.
You can also check the mower's charging dock or charger. The charger is usually labeled with the voltage it is designed for, and it will only work with batteries of that voltage. If you plug a 12-volt battery into an 18-volt charger, the charger will not recognize it and will not charge it.
What happens if you use the wrong voltage battery
Using a battery with the wrong voltage in your mower will damage the electrical system. If you put a higher-voltage battery in a mower designed for a lower voltage, you will overload the motor and the charging circuit, which can burn out wiring and destroy the motor permanently. If you put a lower-voltage battery in a mower designed for higher voltage, the motor will not have enough power to run, and you may damage the battery itself by trying to draw more current than it can safely deliver.
Always match the voltage exactly. If you are unsure, write down the voltage from your current battery or manual and bring that information with you when you shop for a replacement. Most retailers will not sell you a battery that does not fit your mower, but it is your responsibility to confirm the voltage before you buy.
Frequently Asked Questions
Can I use a higher-voltage battery to make my mower more powerful?
No. A higher-voltage battery will damage your mower's motor and electrical system. The mower is engineered to work with a specific voltage, and using anything else will cause permanent damage. If you want more power, you need to buy a mower designed for that voltage.
How long do lawn mower batteries last before I need to replace them?
Most lawn mower batteries last three to five years with normal use and proper storage. Leaving a battery uncharged for months or storing it in extreme heat or cold shortens its life. Charging it after every use and storing it in a cool, dry place helps it last longer.
What is the difference between amp-hours and voltage?
Voltage is the electrical pressure the battery delivers; amp-hours measure how much total charge the battery holds. A 20-volt battery with 5 amp-hours holds more total energy than a 20-volt battery with 2 amp-hours, so it runs longer. Voltage and amp-hours work together to determine runtime and power.
Do all 20-volt batteries work in all 20-volt mowers?
Not always. While many brands use 20-volt as a standard, the physical shape and connector type vary. A DeWalt 20-volt battery will not fit a Makita 20-volt mower, even though both are 20 volts. Always check your mower's manual to see which battery brands and models are compatible.
Is it worth buying a cordless mower if I already have gas mowers?
That depends on your yard size and how many tools you own. Cordless mowers are quieter, require no fuel or oil changes, and are cheaper to operate. But they have limited runtime and are best for yards under half an acre. If you already own cordless tools from the same brand, a cordless mower makes more sense because you can share batteries.