The Voltage Myth: How Tool Brands Made 18V Sound Like 20V

If you’ve ever shopped for cordless power tools, you’ve probably noticed a confusing pattern: some brands sell "18V" tools, while others advertise "20V MAX." Likewise, you’ll see "36V" tools and "40V MAX" tools that look nearly identical in performance.

So what’s really going on here? Let’s decode it.

Behind the Numbers

Lithium-ion batteries, which are used in every modern cordless tool, have two different voltage ratings: maximum and nominal.

Maximum voltage is what the battery measures when it's fully charged.
Nominal voltage is its average operating voltage while the tool is running.

Each lithium-ion cell inside a battery pack produces about 4.0 volts when fully charged and around 3.6 volts while in use.

That means an 18V battery and a 20V MAX battery both contain five cells in series:

5 × 3.6V = 18V (nominal)
5 × 4.0V = 20V (max)

Same cells, same voltage, same power. The only difference is which number the marketing department decided to print on the label.

The 40V vs 36V Trick

The same naming game shows up with outdoor power equipment. You'll see 40V systems from brands like Ryobi, Kobalt, and Greenworks, while others advertise 36V.

Once again, it's the same math:

10 cells × 3.6V = 36V nominal
10 cells × 4.0V = 40V max

Different sticker, identical pack design. Some manufacturers have gone with utilizing two 18V batteries in series to achieve this 36V total, while some use a dedicated 36V/40V battery line; again, no difference in actual output and performance.

How This All Started

When DeWalt (owned by Stanley B&D) launched its 20V MAX line in the early 2010s, it was introducing new marketing under the guise of a new battery platform.

The 20V MAX label sounded stronger than 18V, and for many shoppers, it worked. If you look closely at DeWalt packaging, you'll notice the small asterisk after 20V MAX*. That’s there for legal reasons. In fine print, it reads:

Maximum initial battery voltage (measured without a workload) is 20 volts. Nominal voltage is 18 volts.

That disclaimer is required to comply with truth-in-advertising laws, since 20V MAX refers to the fully charged state, not the voltage while in use. Brands that label by nominal voltage (like Milwaukee, Makita, and Bosch) don’t need the asterisk, because their numbers already reflect real-world operation.

You might wonder why brands like Ryobi, Kobalt, or Greenworks don’t include an asterisk on their 40V tools. The reason is simple: those outdoor power systems were launched as standalone 40V lines, not rebranded from existing 36V platforms. There’s no older “36V Ryobi” system to confuse consumers, so there’s no legal need for a fine-print disclaimer.

In short, it's what you might call marketing voltage inflation. The numbers got bigger, but the power didn't.

What Really Determines Power

Voltage is just one piece of the equation. Real power comes from volts × amps = watts.

That means two 18V tools can perform very differently depending on:

The amp-hour (Ah) rating of the battery
The efficiency of the motor and electronics
The gearing and torque curve of the tool

An 18V Milwaukee M18 FUEL drill can easily outperform many 20V MAX drills because its brushless motor and electronics are simply more efficient.

What about 24V Tools?

24V tools are actually 21.6V nominal. Tools marketed as 24V, such as product lines from Flex and Kobalt, are truly a higher voltage class than 18V, although not by as much as they would have you believe. Looking at the power equation above, we can see that a higher voltage does equal higher power output, all other things considered.

Likewise, 12V (10.6V nominal) product lines such as Milwaukee M12 and Dewalt 12V MAX will naturally be more limited in available power output as compared to their 18V/20V counterparts.

How to Compare Tools the Right Way

Ignore the label and look deeper. The smart way to compare is by checking:

Battery size (Ah rating and number of cells)
Motor type (brushless or brushed)
Tool specs (torque, RPM, impacts per minute)
Runtime tests and reviews

Those tell you far more about a tool's capability than "18V" or "20V MAX" ever will.

Bottom Line

20V MAX = 18V. 40V MAX = 36V. 60V MAX = 54V.

The difference is marketing, not performance.

All lithium-ion batteries operate across the same voltage range depending on their charge level. So the next time you're comparing drills or trimmers, don't get distracted by inflated numbers. Focus on motor efficiency, battery capacity, and overall build quality, because that's where the real power lives.