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.
You Have to Do the Math
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.
36 volts x 50 amps = 1800 watts
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).
Why Can’t You Just Make a 120V Battery?
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.
First: Battery Cells with More Power Density
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.
Second: More Rows of Cells Equals Less Current Per Cell
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:
- 5-cell packs have to generate all that current from just 5 cells. The 15-cell pack distributes it across 3X as many cells.
- 15-cell packs generate more overall heat—even though the individual cells are taxed less. That center row of cells needs to “breathe”.
- 15-cell packs run longer due to more capacity AND having that capacity spread across a higher number of Lithium-ion cells.
Third: The Future Looks Bright
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.