M18 RedLithium Batteries News & Opinion

Seeing Red: Milwaukee M18 RedLithium Batteries

I had the opportunity to speak with Paul Fry, VP of Product Management at Milwaukee Tool, about Lithium-ion technology and just what makes the Milwaukee M18 RedLithium battery the high water mark that everyone else is shooting for. What I found was enlightening… and it might just make you change the way you think about the battery in your cordless tools.

How Does a Lithium-Ion Battery Work?

The idea of the battery has been around for a long time. Lithium-Ion batteries are relatively recent upgrades, but the basic concept is still the same. Take a look at any AA or AAA battery and you’ll notice one side is marked as positive, the other  marked negative. These are called the cathode and anode. Between them is a cell separator that keeps them from touching and shorting out while still allowing electrons to flow. A Lithium based salt compound is the electrolyte that produces the power.

M18 RedLithium Batteries

The “guts” of the battery cell all rolled out!

It starts when we connect the battery to a tool. The connectors make a bridge between the cathode and anode and an electrical current begins to flow between them. That current causes a reaction in the Lithium salt electrolyte which produces positive current, called cations, or more practically, power. The cation produces is a positively charged Lithium ion.

That’s a very basic description of how the process works. For a more detailed explanation that includes much more of the chemistry, check out this page on Physics Central.

Making M18 RedLithium Better

According to Paul, there are 3 critical parts that are required to make a Lithium-ion battery: the battery cell (see above), the pack (houses the cells), and electronics (protects the cells). Among these three components are dozens, if not hundreds, of variables that all affect the performance of the battery. Adjust any one of them, and there is a trade off that has to be made. The secret to making the best Lithium-ion batteries on the planet is finding the right combination of variable adjustments that improves performance and limits trade offs.

The Battery Cell

Look back at the basic idea of the battery cell – cathode, anode, and electrolyte. The easiest way to make a better battery is to simply stuff more of those components into the battery. There’s a trade off – heat. The more you pack in the battery, the more heat is produced. Heat is the number one danger to Lithium-ion performance.

For the M18 RedLithium, the first breakthrough came in the form of the tabs that are on the battery cell. Even today, most have a single tab. Milwaukee added a second and became the first to realize the increase in output that comes from a multiple tab lithium-ion cell.

Designing the Battery PackM18 RedLithium Batteries

When it comes to the design of the housing around the cells, the pack plays a huge role in how much electrical potential can be put in those cells. While the exact details of the M18 RedLithium pack are proprietary, Paul was able to give me some general ideas of what the pack does to help. For starters, it’s the first line of defense to dissipate the heat away from the cells. It also can help to physically dampen the effects of vibration which is a massive consideration in aggressive tools like a reciprocating saw. The design can also help to protect against damage from moisture. We all know that water and electricity don’t mix.

Electronic Communication

Then there are the electrical components to consider. This includes the electronic communication for discharge to power the tool and the charging cycle with the battery charger. If the charge or discharge is too aggressive, it can generate overwhelming heat and limit the life of the battery. For more on things that hurt Lithium-ion battery performance, check out our Top 5 List.

M18 RedLithium Vs. the Competition and Bigger Numbers

News flash. Milwaukee was not the first manufacturer to introduce the 5.0 amp hour battery. They weren’t the second, either. Somehow though, they seemed to be getting better performance than others before the announcement of their own 5.0 that is coming out in November. Why?


Material Considerations

First of all, we need to address the issue of materials. Not all 18V 4.0 amp hour batteries are created equal. Those dozens of variables we talked about earlier each affect performance and every company designs their batteries in different ways. Yes, they’re all lithium-ion, but even the Lithium salt used as an electrolyte can differ. Because of the enormous number of variables, if you could put Ridgid, DeWalt, Makita, and Bosch batteries into a form that would fit into a Milwaukee tool, every one of them would give you different performance from the M18 RedLithium and from each other.

Bigger Numbers

What about when a manufacturer goes from 4.0 to 5.0 amp hours?  They do see a run time increase of 25% compared to their own battery. But what if there was another 4.0 amp hour battery that was already running 25% better run time? You’d have a 4.0 and a 5.0 that give you identical run times albeit from different manufacturers. Not all 5.0 amp hour batteries have 25% greater run time than every 4.0 amp hour battery, it’s only that much better against their own.

M18 RedLithium Batteries

When is an Amp Hour Increase Actually a Performance Decrease?

This realization really woke me up as Paul and I were discussing M18 RedLithium performance. The idea that increasing the amp hour size of the battery can actually produce worse performance seems counter intuitive. Here’s how it works:

Most cordless power tools have an automatic shut down built in to the communications if the battery reaches a certain threshold, typically around 70 Celsius. (158 Fahrenheit). This prevents permanent damage to the battery from overheating.

Now, take a 5.0 amp hour battery that was poorly constructed to deal with the increase in heat. On paper, it may be able to run a rotary hammer for an hour of consistent use. Because of the built in heat protection and the quick rise in temperature, it shuts itself off after just 30 minutes of work during real world use. There’s still some juice left, but you can’t access it until the tool and battery cool down.

This is typically going to be an issue in tools that aggressively use power like rotary hammers, reciprocating saws, and even M18 RedLithium Batteriescircular saws. I’ve had tools shut down on me during stress tests, particularly in the summer months, thanks to an inability to effectively disperse the heat. During the same stress tests, Milwaukee tended to be able to continue on where others had to stop.

Without the proper considerations for power hungry tools, you can actually have a 5.0 amp hour battery that acts like a 2.5 amp hour. Yes, there are batteries on the market like this. Sure, they may have more amp hours there, but the battery doesn’t handle the current as well resulting in disappointing performance.

Concluding Thoughts


Lithium-ion batteries are a complicated combination of physics and chemistry. At the end of the day, most of us just want to know that they work the way they are supposed to when they are popped into the tool. We don’t really care what makes them work, but we do expect the best that’s available for our hard earned money.

One of the really great things for us as users is that we’re far from the end of innovation. The cordless tools that we are using today are still capable of much more performance. It’s just a matter of waiting on the batteries to catch up.


The fact that the batteries we have today work as well as they do is an outstanding improvement over the Ni-Cad batteries of yesteryear. The fact that Milwaukee’s M18 RedLithium batteries are years ahead of some of their competitors? That’s just amazing.

M18 RedLithium Batteries

All of these variables that we have talked about play into performance. Milwaukee and their team of engineers and product managers strive to make the M12, M18, and Fuel products outperform anyone else’s batteries and to produce cordless tools that outperform corded ones. To be sure, there are some other good batteries on the market. On the other hand, Milwaukee’s commitment to disruptive innovation seems to keep them well ahead of everyone else.

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How do they actually ” outperform ” ?

In this review

Pretty much thesame tools. Both the heavy duty brushless oferrings with a freshly charged 4.Read more…