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Dewalt 15Ah Battery – Why its Cell Count and Configuration Matters

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Dewalt recently introduced a new FlexVolt 15Ah battery that works with their 20V Max and 60V Max cordless power tools.

To some people, the 15Ah part is all that matters.

But to many – and the industry – the deeper details hold much significance.

The popular community theory is that the new Dewalt battery pack is equipped with (30) 18650-sized battery cells, each with 2.5Ah charge capacity.

If you do the math, 3.6V x 30 x 2.5Ah = 270 watt-hours.

This could also potentially be a 15-cell battery pack built with 21700-sized Li-ion battery cells, each with 5.0Ah charge capacity. But, the size and weight of the new battery suggests that it’s built with (30) 2.5Ah 18650 cells.

The math with 21700 cells would be: 3.6V x 15 x 5Ah = 270 watt-hours.

According to Dewalt’s published specs, the new FlexVolt 15Ah battery weighs 4.5 lbs. Dewalt has provided dimensional specifications for the new battery: 6.8″ length x 3.4″ width x 3.9″ height.

Dewalt FlexVolt Battery 9Ah Cell Configuration
Dewalt FlexVolt Battery 9Ah and 12Ah Li-ion Cell Configuration

In comparison, Dewalt’s Flexvolt 20V/60V Max 12.0Ah battery weighs 3.2 lbs and measures 5.4″ in length and 3.8″ in height.

The new Dewalt 15Ah battery is larger and heavier than all of the brand’s existing 20V Max and FlexVolt cordless power tool batteries, including their soon-to-be second highest capacity 12Ah battery.

While longer, the new FlexVolt battery should be widely compatible with existing tools given that it nearly matches the height of other high capacity FlexVolt batteries.

In the other post, Big Richard was the first to suggest that this could be a 30-cell battery with 18650 cells, rather than a 15-cell battery with 21700 Li-ion cells.

Why is this important?

The battery cell size, count, and configuration largely dictate its theoretical and practical power and performance output levels.

While power and performance of a tool and battery pairing depends on many factors, it’s convenient to simplify things for the sake of discussion. Following are two generalizations.

If you have a 5-cell battery rated at 3.0Ah charge capacity, and a 10-cell battery also rated at 3.0Ah, the 10-cell battery can drive heavier duty tools and higher demands for longer.

Similarly, if you have a 10-cell 6.0Ah battery with 18650 cells, and a 10-cell battery 6.0Ah battery built with 21700 cells, the 21700 cell-equipped battery will usually be higher-performing.

Here are deeper discussions about battery basics:

Revisiting What an Amp-Hour Means for Cordless Power Tool Batteries, and Other Tidbits

Milwaukee M18 Cordless Power Tool Battery Sizes Explained

Cordless Power Tool FAQ: What Does “Ah” Really Mean?

Milwaukee’s Next-Generation Battery Tech (Advanced Discussion)

As for 18650 and 21700, these are industry stands that describe the diameter (18 or 21 mm) and length (650 or 700 mm) of Li-ion cells.

(In case you’re wondering, a rechargeable lithium-ion battery cell in AA sizing would be 14500, and a rechargeable Li-ion cell in AAA sizing would be 10440.)

Brands shifted to 21700-sized Li-ion battery cells from 18650 because several tech and performance ceilings were reached.

Going by memory, the best 2.0Ah cells from a few years ago topped out at ~25A max current output, the best 2.5Ah cells topped out at ~20-22A max current output, and the best 3.0Ah cells topped out at ~15A max current output.

Heat becomes a greater challenge with higher charge-density cells.

Consider a room that’s filled with kindergarteners to 60% capacity. The kids all had some chocolate and are then asked to leave the room, fast. There’s going to be a lot of energy in that room, and for the most part they’ll exit the room at a comfortable pace. Now fill that room to 100% capacity. If you try to hustle them through the door at the same rate, there might be more pushing, shoving, distractions, and a lot more resistance.

So what do you do if you want to cram even more energy into a room? You build a bigger room.

In 2015, we talked about the end of the road as far as traditional cordless power tool batteries could go. At that time, 15-cell batteries and batteries built with 21700 cells weren’t announced yet.

18V Batteries are Now at 6.0Ah – How Much Higher Can They Go?

It’s amazing when you think about it, that just 6 years ago 18V cordless power tool battery packs were at their limits and none of today’s higher output or higher voltage options were even announced.

Milwaukee’s 15-cell M18 HD batteries were first announced in mid-2015, and Dewalt’s FlexVolt system was announced in mid-2016 with their larger form factor batteries hinted but not formally announced or released until later.

Since then, the trend for professional cordless power tool brands has been to move towards higher voltage systems (e.g. Dewalt Flexvolt, Metabo HPT MultiVolt, Milwaukee MX Fuel) and 21700-equipped batteries (M18 High Output).

This is where things get complicated.

Metabo has a 10.0Ah battery pack:

New Metabo 18V 10Ah Power Tool Battery is “World’s Most Powerful” of its Size

Dewalt also has a 10Ah battery:

New Dewalt 20V Cordless Mowers, Powered by Dual 10Ah Batteries

Dewalt could have introduced a FlexVolt 15Ah battery built with 5.0Ah cells. And they still can. But it appears that they went with 18650-sized 2.5Ah cells.

Let’s look at some specs.

18650 Cell Max Discharge Current

  • Samsung INR 18650-25R (2.5Ah): 20A

21700 Cell Max Discharge Current

  • Samsung INR21700-30T (3.0Ah): 35A
  • Samsung INR21700-40T (4.0Ah): 35A (w/o 80°C temp cut)
  • Samsung INR2170050E (5.0A): 9.8A
  • LG INR21700M50T (5.0Ah): 14.55A at 10-25°C

The LG 5Ah discharge current plummets below 10°C (50°F) and above 25°C (77°F). There could be better 21700 5Ah cells, but these are the best high-discharge ones I could find.

If you ignore cooling considerations, 2X 18650 2.5Ah cells in parallel can deliver approximately the same max current as 1X 21700 3.0Ah or 4.0Ah cell.

This is why some brands’ larger form factor compact (5-cell) battery packs can deliver the power of their higher capacity (10-cell) 18650-based battery packs. For example, a Milwaukee compact M18 4.0Ah battery can be used in place of an M18 XC 4.0Ah battery without power or performance compromises.

Dewalt’s FlexVolt batteries have 15 cells, and can be paired with their 60V Max or 20V Max cordless power tools. But, for the battery to be FlexVolt-compatible, you need 15 cells or multiples of 15.

With each 3.6V cell described as a 4.0V Max cell, 4V x 15 = 60V Max.

Doubling that would give us a 30-cell battery with 20V Max and FlexVolt tool compatibility.

Ignoring cooling and any other considerations, (2) of the aforementioned Samsung 2.5Ah cells could potentially deliver 40A of combined max discharge current, which would approximately match the maximum discharge current ratings of individual 3.0Ah and 4.0Ah cells used in Dewalt’s 9.0Ah and 12.0Ah battery packs.

On paper, (5) Li-ion cells arranged in series deliver 18V and the rated max current capacity. Real-world and engineering limits will be lower.

(10) cells arranged in a 5-series 2-parallel configuration give you 18V and double the charge capacity, but there is also a theoretical doubling of the max discharge current (again, ignoring real-world limitations).

(15) cells arranged in a 5-series 3-parallel configuration give you an additional boost in capacity and max discharge potential.

Since tools are designed around a performance standard, they won’t always be able to take advantage of the extra overhead, but that higher power capacity also means the batteries will run cooler even in demanding use.

New FlexVolt Battery Implications

Now we have 30 cells, does that mean this is a 5-series, 6-parallel battery pack when used in 20V Max tools? This could provide a current and charge capacity boost, possibly even compared to even existing FlexVolt options.

If the battery is switching contacts in the same way as for existing FlexVolt tools, as they physically switch from 20V Max to 60V Max configurations depending on the tool they’re connected to, this would reflect new engineering accomplishments by Dewalt.

When paired with a FlexVolt/60V Max cordless power tool, the 30-cell battery would be arranged in a 15-series, 2-parallel arrangement. In a 20V Max tool, the configuration would likely be 5-series, 6-parallel.

Other brands could potentially follow suit.

It’s unclear how some brands are able to produce competitive 10Ah battery packs, but presumably there are some cells that can deliver the necessary discharge current levels with sufficient cooling considerations. But, based on datasheet specifications for available 21700 5.0Ah cells, the ones we looked at are bested by 2.5Ah cells in parallel.

Is this the way forward? Might other brands have to go to 20-cell 2.5Ah cell arrangements to get to 10Ah, or 30-cell arrangements to get to 15Ah?

What becomes possible at that power level?

An 18V or 20V Max 12Ah battery would be rated at 216 watt-hours. This 15Ah battery is rated at 270 watt-hours, which is a 25% increase in energy.

Are we going to see more 120V Max cordless power tools from Dewalt? Maybe 2x M18 tools from Milwaukee?

At the least, this is a new way to achieve a higher charge capacity for longer runtime.

But, consider what happened in the past when similar advancements were made. What happened when brands stepped up from 5- and 10-cell battery packs to 15-cell batteries? What happened when brands found a new way to push past a charge capacity ceiling to reach new levels?

Milwaukee M18 HD, Milwaukee M18 High Output, Dewalt FlexVolt, Metabo MultiVolt, Makita 18V X2, Bosch CORE/Profactor – every time a battery advancement was made within a cordless system, it paved the way for new cordless power tool developments.

Going from 12Ah to 15Ah in this way is nothing like the bump-up from 3.0Ah to 4.0Ah or 4.0Ah to 5.0Ah just a few years ago.

Think about it – if you’re a user that wants more runtime with fewer interruptions, you can work within your cordless system’s limitations and just buy more batteries and faster chargers.

This could just be about bumping up runtime from 12Ah to 15Ah, but with added size and weight? And, don’t forget that fresh engineering efforts must have gone into these batteries.

There’s going to be more about these batteries. I don’t know what, yet. Maybe a cordless 10″ table saw? Full-size 120V Max dust extractor? Dewalt’s first cordless snow blower?

If this is indeed a 30-cell battery, Dewalt has taken things to a new level, and there’s a good chance they designed it around new cordless power tools or innovations.

And, even if they didn’t, this represents a direction that other brands could go in. Dewalt is raising the ceiling just a little bit, but possibly enough to allow for their next generation of cordless power tool tech.

Back in October 2019, I wrote about how their compact 4Ah battery wasn’t really a big deal. It was welcome, but it wasn’t a huge development since they were already using similar cells in larger battery packs and they already had a compact 3Ah battery.

With this 15Ah battery, everything about it screams “this is a big deal!”

We will be happy to hear your thoughts

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