October 20, 2021

Professional Tool Reviews for Pros

Milwaukee HD High Demand vs DeWalt FlexVolt Batteries

Milwaukee 9.0 Vs DeWalt FlexVolt

Without a doubt, two of the biggest battery-related news items this year have been the DeWalt FlexVolt and the Milwaukee HD High-Demand batteries. It’s reignited the debate between the need for higher voltage and greater amp-hour capacity to extend runtime and power on the jobsite. When it comes to Milwaukee HD High Demand vs DeWalt FlexVolt batteries, we figured the best way to see which was the reigning champ was to test them head to head.

To accomplish this, we grabbed a Milwaukee RedLithium High Demand 9.0Ah battery pack and a DeWalt FlexVolt 3.0Ah battery. The DeWalt FlexVolt battery also works as a 9.0Ah pack at 20V. That makes these two batteries a fairly even match-up.

Milwaukee HD vs DeWalt FlexVolt Battery Capacity

The Milwaukee High Demand 9.0Ah RedLithium battery extends capacity while staying on Milwaukee’s original M18 platform. A simple multiplication problem of nominal volts multiplied by the amp hours will tell you that the Milwaukee 9.0 amp hour battery has a total capacity of 162 watt-hours packed into 15 lithium-ion cells (it’s also written on the underside of the pack). This the only battery currently shipping on the market to reach 9.0 amp hours for handheld power tools.

Milwaukee HD9.0 battery pack

The DeWalt FlexVolt battery has the ability to switch between 20V Max and 60V Max voltages. These are maximum voltages at the highest charge state and translate to 18V and 54V nominal. At 20V Max, the battery runs 6.0 amp hours. At 60V Max, it runs at 2.0 amp hours. There isn’t any other battery available that has the ability to switch voltages. In that, the FlexVolt is truly unique. Dewalt is also planning a 9.0Ah FlexVolt battery pack in early 2017. Do the same math problem we did with Milwaukee, and you’ll find the total capacity of 108 nominal watt hours packed into 15 lithium-ion cells.

Milwaukee 9.0 Vs DeWalt FlexVolt

So when we look at the battery capacity in terms of watt hours (total power availability), we see that Milwaukee has the advantage. However, DeWalt does have a 162 watt hour FlexVolt battery in the works that we expect to be released early next year.

Milwaukee High Demand vs DeWalt FlexVolt Voltage vs Amp Hours

There’s a complex debate between voltage and amp hours that involves a lot of physics and chemistry geek speak. We’re not going to get into all of that right now, but the bottom line is that you have to have both to produce power. Increasing either the voltage or the current flow will increase your available power. Let’s look at this simple equation:

Power = Current x Voltage

To get the same power you can either increase current…or increase voltage. Take your pick. In this way, the higher voltage does not necessarily equate to a higher power tool. That’s especially true given the limitations of a battery pack’s total capacity (measured in watt-hours (Wh). The Milwaukee HD vs DeWalt FlexVolt batteries come pretty evenly matched.

Milwaukee HD9.048-11-189018V9.0Ah162Wh
DeWalt FlexVolt 9AhDCB60920V/60V9.0/3.0Ah162Wh

In theory, if you give two tools identical tasks it should require the same amount of work from both regardless of the volt/amp configuration. So let’s plug in some actual numbers for these batteries:

Milwaukee HD 9.0 Pack Power = 9.0 Ah x 18V = 162 Wh

DeWalt FlexVolt Power = 2.0 Ah x 54V (nominal) = 108 Wh

DeWalt FlexVolt 9.0 Ah Power = 3.0 Ah x 54V (nominal) = 162 Wh

or using the battery in series mode at 20V Max…

DeWalt FlexVolt 9.0 Ah Power = 9.0 Ah x 18V (nominal) = 162 Wh

The reality is you can only go so far before putting the cells in danger, usually due to heat. So is one battery better than the other in this case?

That’s exactly what this Milwaukee HD vs DeWalt FlexVolt comparison aims to find out in order to help you decide!

Milwaukee HD9.0 vs DeWalt FlexVolt: The Test

I’ve taken the DeWalt FlexVolt angle grinder and Milwaukee M18 Fuel angle grinder (Model 2781) and put identical 5-inch cutting wheels from Diablo on them. I’ll see how many cuts I can make through rebar with a fully charged battery.

There are several ways to tackle this test, but I want to mimic what users in the field are most likely going to do. That’s why I’ve chosen to dial in the sweet spot between cutting speed and battery efficiency. I want to cut through the rebar as quickly as possibly without bogging down the tool to do it.

I’ll switch grinders after every cut and ensure they have a minimum of 30 seconds rest before cutting again.

Milwaukee 9.0 vs DeWalt FlexVolt: Results

The DeWalt FlexVolt Grinder clearly has more power than Milwaukee’s, and it showed quickly in testing. I was able to cut efficiently with roughly a 2 second advantage on average. That varied as the cutting wheel wore down, however. The average cut for the FlexVolt took about 17 seconds and right at 19 seconds for Milwaukee. There were both faster and much slower cuts for each throughout the test.

cutting rebar with a grinder

At no time did either grinder give up due to heat build up. Also, neither tool (or its battery) felt so hot to the touch that appeared to be in danger of shutting down.

After running the Milwaukee High Demand vs DeWalt FlexVolt comparison, the FlexVolt grinder finally gave up after 50 cuts. Milwaukee’s Fuel grinder lasted through 68.

So why didn’t Milwaukee’s 50% greater battery capacity result in 50% more cuts?

That answer lies in the power of DeWalt’s 60V Max grinder. Since it didn’t have to work as long as Milwaukee to make each cut, it finished the job faster. When you look at the total time each grinder had to work, it becomes more clear. DeWalt had to work for roughly 14 minutes, 10 seconds. Milwaukee worked 21 minutes, 30 seconds – 52% longer than the DeWalt.

The X-factor in all this is that the Milwaukee HD was much more efficient vs DeWalt FlexVolt when it came to using up the abrasive wheel. I switched them out after 30 cuts when DeWalt’s was getting closer to the end of its useful life (but before it was completely shot). The Milwaukee grinder using the Milwaukee High Demand 9.0 battery still had plenty of life left.

Milwaukee 9.0 vs DeWalt FlexVolt: Two Lines of Thought

Both Milwaukee and DeWalt have very valid claims you need to seriously consider in your purchasing decision. First, DeWalt has clearly raised the bar on how much power they’re getting from many of the new tools in the FlexVolt line. The batteries are backwards compatible with your DeWalt 20V Max products. They also have a 162 watt hour battery on deck. You can’t, however, use your 20V Max batteries in a FlexVolt tool, so you are getting into a new battery and tool system.

For now, Milwaukee undeniably has higher battery capacity and run-time. You also won’t have to buy into a new battery platform in order to use all your M18 tools. They certainly deliver a lot of power on their 18-volt grinder, but it’s exceeded handily by the DeWalt FlexVolt grinder in our testing. Milwaukee is committed to the 18V platform, and it will be interesting to see what they can do in terms of power with those tools. As lithium-ion battery cell technology continues to improve, all of these power concerns may go away altogether.

The Bottom Line

This is just one test among hundreds that we could have chosen from across several different tools. Every user’s needs are going to be a little bit different, so you need to take the information you’ve learned here, and decide for yourself if one battery platform is better for you than the other.

There are a lot of variables in play thanks to the wide variety of tools that are powered by both batteries. At the end of the day, if staying on one battery platform and knowing all your tools will work with all your batteries is most important to you, Milwaukee is the way to go. You’ll still get great performance. If getting the greatest amount of power is the most important factor, DeWalt may have the edge for now. You’ll still get decent run time, and that will improve further when the new 3.0/9.0Ah battery arrives.

But then there’s the Metabo 36V 9-inch grinder… A conversation for another day perhaps.

Tell us what you think! Sound off on Facebook, Twitter, and Instagram!

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Apples to Apples and Oranges to Oranges. Which would you rather have. Higher Voltage or Higher Current ? Higher Voltage equates to the ability for higher RPMs and Higher Current equates to the ability for longer runtimes. Laws of Physics here. Then there is how each Manufacturer manages the efficiency of these quantities in their tools. Such as Brush versus Brushless motors and power management and such. My choice would be the Higher Voltage. But then that is me.


“So why didn’t Milwaukee’s 50% greater battery capacity result in 50% more cuts?” It’s simple, it didn’t have 50% greater capacity. When you talk about capacity you’re really talking about stored energy, and stored energy is measured in a unit like joules or watt*hours (power*time). Amperes is simply a measure of current and doesn’t really account for the amount of work you can do with any battery. You did bring it up earlier in that both the larger DeWalt and Milwaukee batteries are 162Whr, that’s really what matters. Stepping up to a higher voltage means lower wiring and motor winding… Read more »


These comparisons don’t make sense. You’re comparing a 9ah 20v usage to a 2ah 60v usage. You should hook the flexvolt battery to a 20v grinder instead of a 60v grinder for a more even comparison, and now that the dewalt 9ah battery is out, update the competition with a new test.


grinder wheel usage seems to point to applied force inconsistency…


You are comparing a 9 amp hour to a 6 amp hour. Factually incorrect to say Milwaukee was more “efficient”. The converse is true. Compare the DW 9 AH for fair comparison

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