Flex 24V Stacked Lithium Battery: A Closer Look at the Pouch Cell Upgrade

Introduction

Flex’s new 24V Stacked Lithium batteries are the company’s latest take on cordless power, built around state-of-the-art pouch cell technology rather than the traditional round cells used in its standard packs. Flex claims a higher power output, a longer run time, faster charging, and all of it in a smaller package.

To see whether those claims hold up, the stacked lithium packs were put head to head against Flex’s own round cell counterparts in a demanding cutting task. The short version: the stacked packs came out ahead in every size class tested.

What Makes Stacked Lithium Different

The key to the performance gain lies in the cell construction. Flex has placed connection tabs inside the battery pack, which allow a greater energy flow than traditional round cell packs. The result is the power needed for heavy tasks without producing dangerous levels of heat.

Peak discharge tells much of the story. When comparing maximum watts at peak discharge, meaning the battery’s highest point of power, the stacked lithium packs clearly fly past their round cell predecessors.

How the Test Was Run

The comparison was deliberately simple and repeatable: five cuts through number five rebar using a cut-off saw. Three stacked lithium packs were tested, at 3.5Ah, 6Ah, and 10Ah, and their average results were compared against the same five cuts made with 5Ah, 8Ah, and 12Ah round cell packs.

Testing like this matters because rebar cutting is one of the more demanding tasks you can ask of a cordless tool, so differences in power delivery tend to show up clearly rather than being masked by an easy workload.

Real-World Results: Cutting Speed and Blade Wear

The stacked lithium packs delivered a measurable advantage across the board:

• 3.5Ah stacked vs 5Ah round cell: a 9.4% increase in cutting speed, despite the stacked pack being smaller.
• 6Ah stacked vs 8Ah round cell: a 17.1% increase, the largest gap of the test.
• 10Ah stacked vs 12Ah round cell: a 15.3% increase, a slight drop from the mid-size pair but still a clear gain.

The felt difference was described as modest but real: the cuts went through noticeably quicker, and both battery types delivered strong, consistent performance.

Blade wear also told an interesting story. With the 12Ah round cell pack, the cutting disc wore down too far partway through the third cut and had to be swapped out. On the second attempt with a fresh disc, all five cuts were completed. With the stacked lithium packs, the full run went through with far less disc sacrifice, and the difference in blade wear between the two battery types was quite visible.

Who Should Upgrade

If you already own Flex 24V tools and regularly push them through demanding work like cutting, grinding, or other high-draw applications, the stacked lithium packs make a compelling case. You get more power in a smaller, lighter package, faster charging, and, based on this testing, quicker results with less wear on your accessories.

For lighter-duty use, the gains will be less dramatic, but the smaller size and faster charging alone are worth considering if you value handling and turnaround time on the job.

Conclusion

Flex’s 24V Stacked Lithium batteries back up the company’s claims with hard numbers: higher peak power output, faster cutting across three size classes, less blade wear, and a smaller form factor. For anyone invested in the Flex 24V platform who wants more from their tools, the stacked lithium line looks like a genuine step forward rather than a marketing refresh.