Professional Tool Reviews for Pros

We talk about the cordless job site pretty frequently. But in the corded vs cordless tools question—can battery truly render the cord obsolete? The math doesn’t add up, right? Actually, it does. As manufacturers push into more powerful cordless tools, the concept of switching out your corded tools without power trade-offs is compelling.

We had to stop and think when asked how can cordless tools replace corded tools? The math didn’t—at first glance—seem to add up. The initial question came through on our Milwaukee RedLithium High Output Battery article, and it’s a really good one. Here’s the rationale:

120 volts x 15 amps = 1800 total watts

18 volts x 15 amps = 270 total watts

36 volts x 15 amps = 540 total watts

…and we can keep going, of course. Any cordless tool producing 15 amps can’t possibly be as powerful as a 15-amp corded model. There must be something more.

There is—and we see it with both automotive and marine batteries. These often produce over 1000 cranking amps from a 12V product! In reality, they can technically produce these amps with just 7.2 volts!

So how can cordless tools replace corded tools and have the same power capabilities? They use or produce more current. Much more. Running as many as 100 amps to power a tool seems awfully high, but that’s exactly what’s going on in the battery.

18 volts x 100 amps = 1800 total watts

Notice that as you increase the voltage, the extra current you need comes down.

In order for the battery pack to only provide 15 amps of current to match what you get out of the wall, it would also have to be wired for 120 volts (DC).

Keep in mind that many manufacturers list a “Max voltage“, which is the voltage at the pack’s highest charge state. It quickly drops ~10% down to its “nominal” voltage where it operates most of the time. So, you’re looking at a tool that would be 133V Max to match the 120V coming out of your wall.

In case it comes up on Final Jeopardy, that would be sets of 37 cells!

While some outdoor power equipment does indeed run at 120V (Max), it probably doesn’t need to. Some increase in voltage helps, but modern battery packs can handle the higher current output.

When I spoke with Paul Fry, Cordless Guru for Milwaukee Tool (my title for him, his official title is VP of Product Management), he gave me a little more insight into how cordless tools are replacing corded tools. He said the original batch of lithium-ion tools that came out years ago could only produce a few hundred watts out. With better cell and tool technology, manufacturers can now produce a few thousand watts out.

And it only gets better when you factor in improvements like new 21700 lithium-ion battery cells.

The question used to be how to manage high current output with enough runtime. Getting 1800 watts to exceed 15-amp corded tools is not only doable, but it’s also effective. Manufacturers have now made significant strides in run-time thanks to better cell technology. We’re also seeing larger battery packs that use as many as three parallel rows of cells.

The primary difference between an 18V pack with 5 cells and one with 15 cells is three-fold:

The future could hold additional improvements as well. We’re seeing news of solid-state battery technology and the use of graphene technology in lithium-ion to improve charging speeds. The use of silicon also promises faster charging and greater power density for all Lithium-ion battery types. This could also yield more output beyond what you can get from a typical 15A wall circuit.

On the clock, Kenny dives deep to discover the practical limits and comparative differences for all kinds of tools. Off the clock, his faith and love for his family are his top priorities, and you'll typically find him in the kitchen, on his bike (he's an Ironman), or taking folks out for a day of fishing on Tampa Bay.

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My experience with Milwaukee Fuel tools is that with greater power comes greater size-more added gearing is needed to take advantage of the 18 volt battery-which I am starting to think will be the dinosaur of tool technology.

How exactly does a lithium-ion battery use or produce more current?

Something else to consider is the major safety benefits of a cordless tool. Drop it in water, no one is electrocuted. Release the trigger and the blades/bits etc. stop spinning/moving almost instantly. On top of that, we have the “Roll out, Roll up” time saver. When you add up all the time it takes when you get to the job every morning, of rolling out the cords and hoses, filling the air, if using a generator you need to fill it with gas, all of this adds a lot of time before you can drive one nail or cut one…  Read more »

Quick edit: “So, you’re looking at a tool that would be 133V Max to match the 120V coming out of your wall. In case it comes up on Final Jeopardy, that would be sets of 37 cells!”

Li-ion cells are generally rated at a nominal voltage of 3.6v, so 120v / 3.6v = 33.33333 cells. Let’s call it 34 cells for 122.4v, NOT 37 cells (you almost cost someone Final Jeopardy). The MAX designation comes from rating the cells at 4v, so the same hypothetical 34 cell battery would be 136v MAX.

Great article explaining power is volts * amps!

A couple of extra points- circuit breakers are all derated by 20% so that if the breaker says 15 amps it’s only going to provide 80% of that. Looks like battery power won’t have this hard limit.

And secondly more current means larger wires, which means bigger and heavier motors and tools. This is what’s driving higher voltage batteries where the same power requires less amps. There’s also an advantage to deliver the amps right at the tool regarding conductor size.

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Professional Tool Reviews for Pros