The Difference Between an 18v and a 20v Drill

Which is More Powerful?

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How many times have you seen a discussion in an online forum or on a social media post where people were arguing about which drill is more powerful, 20v or 18v? Sadly, for me, the answer is far too many to count. The debate usually breaks down into a back and forth between those who understand how batteries work and those that inevitably end up sounding like Nigel Tufnel on why his Marshall amp is one louder: “These go to eleven.”


In order to understand the difference (if any), we need to first take a look at how a battery works and what’s inside that battery pack you plug in to your drill.



Voltage is simply a measure of potential energy. If we look around, there are lots of different devices that are designed to operate at different voltages. A wall socket in the US supplies around 120 volts while that AA battery in your flashlight is rated at 1.5 volts. The important thing is that voltage is always measured between two points- the positive and negative terminals on your battery.


How Does a Battery Work?

When we connect a battery pack to our drill and switch it on, chemical reactions start happening due to the nature of positive and negative charges being attracted to one another. Positive electrons flow from the negative terminal through the drill and back to the positive terminal of the battery. The higher the voltage, the more current a battery will produce when it’s connected into a circuit and a bigger voltage usually means more power.

So you’re saying that Nigel was right after all?

In a word, no.


The Battery Pack

An 18v or 20v battery pack is made up of individual battery cells and are always put together in groups of five. The five cells are wired together in series and then each group is wired in parallel to other groups to increase the amp-hour rating of the pack.

Every battery cell has two voltage ratings: nominal and maximum. The amount of voltage, or potential energy, is slightly lower when the battery is in use as compared to when it is fully charged and idle. The nominal voltage of a battery cell is 3.6 volts. The maximum voltage when fully charged is about 4 volts. I’m sure you can see where this is going, but let’s do the math. 5 cells @ 3.6 volts each = 18 volts. 5 cells @ 4 volts each = 20 volts.


Let’s Test Them

With the help of my trusty volt meter, we can see that a fully charged Milwaukee 18v battery measures 20.8 volts and a fully charged DeWalt 20v MAX battery measures 20.6 volts. So they are virtually the same.


What’s the Difference?

So it really comes down to the label and the decisions of the marketing department. You’ll notice that DeWalt, Porter Cable and Black + Decker are labeling all of their 20v products with the 20 volt MAX insignia while most all of the other major brands like Milwaukee, Makita, Bosch, Ryobi, et al go with the 18 volt rating. Maximum or nominal- that’s is the only difference.

Before you start bashing DeWalt for shady marketing tactics, note that all of the manufactures use the 12 volt rating for their 3 cell products. 3 cells @ 3.6 volts each = 10.8 volts. I guess 12 volts has a better ring to it than 10.8. And as an added bonus, these go to twelve.     

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Steve Wright

Steve Wright is a general contractor who over the last 30 plus years has built hundreds of new homes, ranging from first time affordable homes to multi-million dollar custom homes and everything in between.

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    There is so much to learn from your site, having come from a technical background, I really like the kind of information you are sharing on this blog. Thanks for educating us.

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