Battery basics

There is a lot of confusion about how motor voltage affects power and run time versus the size and capacity of the battery pack being used. Here’s a simple guide to understanding batteries.

The voltage of any cordless tool is not the overriding factor that determines power and run time.

A tool’s motor can only draw as much energy as the battery pack can safely put out, so the performance of this energy source is integral to the tool’s performance.

Unlike fuel in a gas tank, which can be drained as fast as desired, battery cells have a limit to their output. Li-ion chemistry offers great storage capacity, but its heat management is a limiting factor. Drawing too much current can dangerously overheat battery components, so cordless tools and battery packs have shut-off features to protect against overdischarging and overheating. Heat management is also the reason hot batteries and high-capacity battery packs take a long time to charge.

Batteries with higher amp-hour ratings have more fuel in the tank.

The unit of measure for comparing batteries of the same voltage is an amp-hour (Ah). Tool batteries typically are made up of 3.6-volt lithium-ion cells. Ten cells wired together in series make up a 36-volt assembly known as a stack. If the cells are rated at 2.0 Ah, you would have a 2.0-Ah, 36-volt battery pack. For even more capacity, another 36-volt stack could be wired parallel to the first stack, creating a 36-volt battery pack and doubling the Ah rating to 4.0. Three stacks together would triple the Ah rating, and so on.

For optimal storage capacity, a bigger battery is generally better, but only until its weight starts to take away from the tool’s ergonomics. That’s why the largest battery packs (up to 30 Ah) are carried on backpacks, with corded connections to the tools they power.

For a battery pack of any voltage to offer more power or a longer run time, its storage capacity must be increased.

Higher-volume energy output (power) or longer-lasting energy output (run time) can be achieved by adding

• more individual battery cells to help share the load;
• larger cells with increased capacity;
• cells of higher energy density with increased capacity; or
• any combination of the above.

More or bigger cells built into a pack are easy enough to visualize (see illustration below), while energy density is simply how much electricity an individual battery cell can hold. The more a cell can store, the higher its density.

What’s inside a battery pack?

Buying strategies

Choosing the right tool or battery platform to fit your needs can be a big decision. Regardless of which tool you choose, it is worth buying a spare battery pack to minimize downtime when you want to be working.

Look for outdoor tools that work with your existing battery packs.

If your favorite power tool brand has the equipment you’re looking for, this is a logical place to start. This approach may save you some money as you build your tool collection, but make sure the battery packs that you have are strong enough to power the tools you need. DeWalt, Milwaukee, and Ryobi all offer a variety of outdoor tools, but the brand with the widest range of fully compatible tools is Makita, with dozens of available models. For 36-volt power, almost all of Makita’s outdoor tools use two of its standard 18-volt battery packs; a few of its compact tools run on just one pack.

Higher voltage is great for big jobs.

Some outdoor equipment brands, often found in big-box home centers, offer tools in the 36-, 54-, and 72-nominal-voltage classes, though brands use different “maximum” voltage numbers for naming purposes. In my experience, the sweet spot with these tool lines is the 54-volt class. The 72-volt tools usually come in a kit with a compact battery pack that has the same capacity as that of the brand’s 36-volt tools, and they are not necessarily more capable than lower-voltage tools. I’ve had great results with a few exemplary brands in this category, including the Echo 58V and Ego 56V lines. Ego is recognized as the brand to beat when it comes to battery mowers, and it goes bigger than most with higher-capacity battery packs optimized for its full-size mowers and snowblowers.

Professional-grade tools are a worthwhile investment.

If you spend a lot of time using outdoor equipment, consider the top pro brands. Stihl and Husqvarna produce efficient tools in the capable 36-volt class, and both offer a wide range of models in different performance and price tiers. Overall, Stihl shows a greater breadth and depth of battery-powered tools, including some unique compact tools that run on 10.8-volt packs. Stihl is the company that first converted me to outdoor battery power on the job back in 2011 with its introduction of a fully legit 36-volt chain saw that opened my eyes to the future of outdoor power equipment.

Battery power is cleaner and greener

Handheld tools powered by battery packs offer several advantages over those that burn fossil fuels.

There’s no need to buy, transport, or store gasoline. If you’re used to two-stroke tools, you will be happy to say goodbye to the routine of properly mixing in oil, then trying to use up the fuel before it goes bad within several weeks—or buying premixed fuel that costs about $30 a gallon.

Battery-powered tools offer low- to no-maintenance operation. They do not require yearly maintenance or engine tune-ups, and you won’t need to winterize them at the end of the gardening season. There’s no idle screw to fiddle with, and no high and low carburetor-adjustment screws.

The tools are quieter and often safer. There is no toxic exhaust to breathe, no screaming engine noise within arm’s length, and no hot muffler to burn yourself on. Many of these tools are quiet enough to be used without hearing protection.

Battery-powered tools offer point-and-shoot simplicity. Push the ON button if the tool has one, then simply pull the trigger to operate. You won’t have to set a choke, pull a cord to start the engine, wait out a flooded carburetor, or restart the engine after every time you set the tool down.

These tools run only when you pull the trigger, with no noisy, fuel-wasting idling time. As an added benefit, most handheld cutting tools have an active brake that stops the tool instantly when the trigger is released, so you don’t have to wait for the tool to coast down. A tool that is silent between tasks makes it much easier and safer for the user to communicate with others.

What are the cons? All you really give up is the all-day run time of a gas engine and the extra power needed for commercial-sized tools such as large chain saws, which still require high-performance two-stroke engines. Other than that, battery-powered outdoor equipment is available with capabilities suitable for almost any gardening job.