18V vs 20V: Same Battery, Different Label

Short answer: 18V and 20V cordless tools run on the same voltage. A "20V MAX" battery and an "18V" battery of the same generation hold the same five lithium-ion cells. One brand prints the voltage measured off the charger. The other prints the voltage under load. No tool is more powerful because the label says 20V.

That doesn't mean the batteries fit each other. DeWalt's 18V packs and its 20V MAX packs use completely different mounts, so a 20V MAX battery won't slide onto an 18V tool however well the voltages match. The problem is mechanical, not electrical, and that's why an adapter fixes it.

Are 18V and 20V the Same Thing?

Electrically, yes. Every lithium-ion cell in a power tool battery has a nominal voltage of about 3.6 volts. Wire five in series, which is standard for this class of tool, and you get:

5 cells × 3.6 V = 18 V nominal

Measure that same pack straight off the charger, before any load hits it, and each cell reads closer to 4.0 volts:

5 cells × 4.0 V = 20 V maximum

Both numbers describe one battery. 18V is what it gives you while you're working. 20V is what it reads sitting still.

DeWalt says this themselves. The footnote on every 20V MAX battery page reads:

"Maximum initial battery voltage (measured without a workload) is 20 volts. Nominal voltage is 18."
See for yourself: DEWALT, 20V MAX 5.0Ah battery specification

Milwaukee, Makita and Bosch print the nominal figure instead. Same battery, different marketing call.

Can You Use a 20V Battery on an 18V Tool?

Not on its own, but yes with an adapter. This is what most people are really asking, and the answer has two parts.

Voltage isn't the obstacle. An 18V tool runs perfectly well off a 20V MAX pack because they're the same 18V nominal system. The obstacle is the battery mount. DeWalt's older 18V tools take a stem pack that slots up into the handle. A 20V MAX pack rails onto a foot. The two shapes have nothing in common, so the battery simply won't attach.

An adapter closes that gap. It takes the 20V MAX pack on one side and presents the 18V stem fitting on the other, so a current lithium battery can run a tool built for a platform DeWalt stopped making years ago.

DeWalt 20V to DeWalt 18V Battery Adapter

It works the other way round too. Running an 18V pack on a 20V tool is the same job in reverse and just as ordinary. A Makita 18V battery will run a Craftsman 20V tool, for example. There's no voltage gap to close in either direction. Only the mount stands in the way, and that's a solved problem.

Which direction is available depends on your exact pair of platforms. The finder at the bottom of this page will tell you.

DeWalt build an adapter like this themselves, which settles any question about whether bridging two platforms is a sensible thing to do. Their DCA1820 is described on DeWalt's own site as:

"Allows for use of 20V MAX* lithium ion batteries in most 18v DEWALT* tools."
See for yourself: DEWALT, DCA1820 battery adapter

So the principle isn't in dispute. The manufacturer builds one. What differs is coverage: DeWalt's adapter bridges DeWalt to DeWalt, while ours bridge 38 brands in both directions, so the batteries you already own can run whatever tools you actually have.

DeWalt 18V vs 20V MAX at a Glance

The mount is the only row that changes anything you can feel. Everything electrical is one class of battery described two ways.

Why Do Brands Print Different Numbers?

Marketing, mostly. DeWalt launched its lithium platform in 2011 and chose to advertise the maximum reading rather than the nominal one. On a shelf lined with 18V competitors, "20V MAX" stood out. Both figures are true. They're taken at different moments.

Several markets now require the nominal figure to appear as well, which is why you'll often see "20V MAX" in large type and "18V nominal" in the small print on the same battery.

What Actually Matters When Choosing

Between a tool badged 18V and one badged 20V, the voltage tells you nothing useful. These do:

• Amp-hours (Ah). How long the battery lasts before it needs charging. A 5.0Ah pack runs roughly twice as long as a 2.5Ah pack on the same tool.
• Motor design. Brushless motors make more torque and run cooler than brushed ones at the same voltage.
• Tool electronics. Overload protection, speed control and heat management matter far more in real work than any labelling difference.
• The platform you already own. Usually the biggest factor, and the one an adapter can change.

Common Questions

Are DeWalt 18V and 20V batteries interchangeable?
Not on their own. Same nominal voltage, different mounts. With an adapter, a 20V MAX pack runs an 18V DeWalt tool. DeWalt sell an adapter for this themselves and ours does the same job.

Will an 18V battery work on a 20V tool?
Yes, with the right adapter. An 18V pack already supplies everything a "20V MAX" tool needs, because both are 18V nominal systems. A Makita 18V battery on a Craftsman 20V tool is a common pairing. The adapter only solves the mount.

Is 20V more powerful than 18V?
No. It's the same battery measured at two different moments, once under load and once at rest. Power comes from the motor, the electronics and the amp-hours.

Is DeWalt 20V MAX the same as Milwaukee M18?
Both are 18V nominal systems, so electrically they're the same class. They aren't physically compatible, and each brand's batteries fit that brand's tools unless you use an adapter.

Does a 20V MAX battery ever really deliver 20 volts?
Only for a moment, unloaded, straight off the charger. Pull the trigger and it settles to about 18V, which is why that's the figure used for the tool's real rating.

Can I use a battery from a different brand entirely?
Yes, with the right adapter. Most 18V and 20V MAX platforms across brands share the same nominal voltage. What differs is the fitting.

Find the Adapter for Your Battery

If your batteries are on one platform and your tools are on another, an adapter costs a fraction of replacing either. Tell us what you own and we'll show you what fits.

Match your battery to your tools