Battery platforms
Cordless Outdoor Tool Batteries Explained: Volts, Amp-Hours and Watt-Hours
Battery mowers, trimmers and blowers are sold on big numbers: 40V, 56V, 60V, 80V, 5Ah, 7.5Ah. Those numbers matter, but they are easy to misread, and some of them are labeled differently from brand to brand. Here is how to read battery specs, compare platforms honestly, and figure out how much battery you actually need.
Quick answer
- Volts roughly indicate the tool's power class. Amp-hours (Ah) indicate fuel-tank size.
- Watt-hours (Wh) = volts × amp-hours. It is the best single number for comparing total energy between batteries.
- Nominal vs max voltage: some brands label the peak voltage, others the nominal. The same cells can be marketed as different numbers.
- Voltage does not guarantee performance. Motor design and tool engineering matter as much.
- Choose a platform for the full set of tools you will need, not just the first one you buy.
The three numbers that matter
Volts (V)
Electrical "pressure." Higher-voltage platforms generally support more powerful tools, all else being equal.
Amp-hours (Ah)
Capacity at that voltage. A bigger Ah number usually means longer runtime within the same platform.
Watt-hours (Wh)
Total stored energy. Volts times amp-hours. The fairest way to compare batteries across platforms.
If you remember only one formula, make it this one: Wh = V × Ah. A 40V 5Ah battery holds about 200 Wh. An 80V 2.5Ah battery also holds about 200 Wh. They store roughly the same energy, delivered at different voltages.
Max voltage vs nominal voltage
Lithium-ion cells have a fully charged peak voltage and a lower "nominal" voltage they sit around during use. Some brands advertise the peak figure, often with the word "max," while others advertise the nominal figure. That is why two batteries with very similar internal cells can be sold as different voltages.
Common examples include battery classes marketed as 18V and 20V max, which are generally the same voltage class, and 36V and 40V max, which likewise overlap. Read the small print on the battery label, which often shows nominal voltage and watt-hours, before assuming one platform is "more powerful" than another based on the headline number.
When two brands' voltage labels are hard to compare, look up the watt-hour rating of the battery. It is often printed on the battery label or in the specifications, and it cuts through the marketing.
Power vs runtime
Voltage relates to the power a tool can deliver. Watt-hours relate to how long it can deliver it. A high-voltage battery with low capacity may power a strong motor for a short time; a large-capacity battery at modest voltage may run a light trimmer for a long time.
Runtime also depends heavily on the load. A leaf blower on turbo or a mower in tall, wet grass draws far more power than the same tool at low speed in light conditions. That is why runtime claims on the box rarely match real use, and why the honest answer to "how long will it run" is "it depends."
Batteries in cold and hot weather
Lithium-ion batteries are sensitive to temperature. In cold weather, a battery delivers less power and less runtime until it warms up, and many chargers will not charge a pack that is too cold or too hot. In summer, a pack left in direct sun or a hot vehicle can overheat, and a battery that has just finished a hard job may need to cool before the charger will accept it.
- Bring packs indoors between uses in cold weather, and let a cold pack warm to room temperature before charging.
- Keep packs shaded on hot days, and avoid leaving them in a closed car or truck bed.
- Expect shorter runtime on cold autumn mornings for leaf blowers and trimmers.
Your manual lists the operating, charging and storage temperature ranges for its batteries; they differ by brand.
Typical platform classes for outdoor tools
These are broad groupings, not brand rules. Individual tools vary widely.
| Voltage class (as marketed) | Typical outdoor tools | Notes |
|---|---|---|
| 18V / 20V max | Light trimmers, compact blowers, hedge trimmers, small chainsaws | Often shared with drills and other shop tools. Some brands pair two packs for bigger tools. |
| 36V / 40V max | Mowers, trimmers, blowers for typical suburban lots | A common outdoor-focused class across several brands. |
| 56V to 60V class | Mid-to-large mowers, strong blowers, trimmers | Outdoor-focused platforms aiming at gas-like performance. |
| 80V class and up | Large mowers, backpack blowers, heavier chainsaws, riding mowers | Top power classes; packs are heavier and cost more. |
How much battery do you need?
Start with the job, not the battery.
- List your tools and jobs. Mowing, trimming and blowing in one session? That is three tools drawing from the same packs.
- Estimate the session. How long does your current routine take with gas tools?
- Check the manufacturer's runtime for the specific tool and battery size, treating it as an optimistic number.
- Plan for at least two packs if your sessions are longer than one battery lasts, so one charges while you use the other.
- Consider charger speed. A rapid charger can matter as much as a second battery for long sessions.
Browse 40V-class outdoor batteries on eBay
Choosing a platform
Batteries are usually not interchangeable between brands, and often not between a brand's different voltage lines. That makes the platform decision more important than any single tool.
- Tool range: does the platform offer every tool you are likely to want in the next several years?
- Battery sizes: are there small packs for light tools and big ones for mowers and blowers?
- Shop tool overlap: if you already own a brand's drills and saws, its outdoor line may share batteries.
- Availability: can you buy batteries and chargers locally if one fails?
- Longevity: how long has the platform been around, and are older tools still supported? Our guide to buying a discontinued charger covers what happens when they are not.
- Warranty: battery warranties are often shorter than tool warranties. Read both.
Pick one outdoor platform that covers mower, trimmer and blower, buy at least one large battery and one medium battery, and grow the system from there. Mixing platforms means mixing chargers and spares.
Bare tool or kit?
Once you own a couple of batteries, buying "bare" tools without batteries is often cheaper. But kits sometimes include a battery and charger for less than buying them separately, especially during sales. The math depends on the platform and the moment; our post on bare tool or full kit walks through it.
Browse bare-tool cordless trimmers on eBay
Battery care basics
- Charge and store batteries indoors within the temperature range the manual lists; avoid hot cars and freezing sheds.
- Let a hot battery cool before charging, as the manual recommends.
- Store for long periods at the partial charge level the manufacturer recommends.
- Use only the manufacturer's charger or an approved one.
- Stop using any battery that is swollen, cracked, leaking, overheating or has been dropped hard, and recycle it at a proper battery drop-off.
- Never use adapters to force batteries into tools they were not made for, unless the tool manufacturer approves it.
Shop battery storage bags on eBay
Third-party and used batteries
Off-brand replacement batteries are widely sold for popular platforms. Some may perform acceptably; others may lack protection circuits, have overstated capacity, or void the tool warranty. Lithium batteries carry real fire risk when poorly made or damaged. If you consider used or third-party packs, read why mixed battery lots need skepticism and look for recognized safety certifications on the listing.
Frequently asked questions
Is an 80V tool always more powerful than a 40V tool?
Not always. Higher voltage allows more power, but motor design, battery capacity and how the tool is built matter too. Compare the tool's performance specs and watt-hours, not just the voltage.
Are 18V and 20V max batteries the same?
They are generally the same voltage class; 20V max describes peak voltage while 18V describes nominal. They are still not interchangeable between brands.
Does a higher amp-hour battery make a tool stronger?
Mostly it makes it run longer. In some tools a larger pack can sustain high output better, but the main gain is runtime.
Can I use a different brand's battery in my tool?
Not without an adapter, and adapters can void warranties and create safety risks. Stick to batteries approved by the tool manufacturer.
The bottom line
Read volts as the power class, amp-hours as the fuel tank, and watt-hours as the fair comparison number. Watch out for max vs nominal labeling, treat runtime claims as best-case, and choose a platform for the whole range of tools you will need. Look after the batteries well and they will look after the tools.