DeWalt Battery Comparison: Power Stack vs XR vs FlexVolt Under Real Drilling Load

Introduction

DeWalt’s newer Power Stack line has changed what a compact battery can do. In a hands-on drilling test using a 3-3/8 inch auger bit through a 4x4 and dimensional lumber, the differences between four popular packs were striking: the 5Ah Power Stack, the 1.7Ah Power Stack, the 9Ah FlexVolt, and the 5Ah XR.

The test focused on power output rather than runtime. Amp hours tell you how long a battery lasts; voltage sag under load tells you how hard it can push. The less a battery’s voltage drops while drilling, the more amps it is delivering. Bigger, slower sag means more usable power at the tool.

How the Test Worked

Each battery was run in speed level one on drill mode, driving the same large auger bit into a 4x4 and then into dimensional lumber. A voltage lead connected to each battery tracked how far the voltage sagged under load, giving a direct picture of power delivery rather than capacity.

The 2Ah reference battery failed to finish both cuts, which set a useful baseline. From there, every pack revealed its character: some held voltage impressively, others cut out before the hole was done.

The Star of the Show: 5Ah Power Stack

The 5Ah Power Stack is a little larger and heavier than expected, but its pouch-style cells are built for high discharge rates. In size terms it sits between formats: about the same footprint as a 4Ah compact, with thickness closer to a 6Ah pack.

On the drill it was a different league. It powered through both the 4x4 and dimensional lumber with serious speed, holding low 18s to high 17s volts under load in the dimensional lumber cut. That is remarkable voltage hold for a pack this size, and no 6Ah or 8Ah pack in the test matched its amp output relative to its weight.

If you want a smaller, lighter battery that delivers all the power a 20V tool can ask for, this is the one that stands out. The trade-off is runtime: at 5Ah it will not last as long as the high-capacity packs on long jobs.

The Surprise Contender: 1.7Ah Power Stack

The 1.7Ah Power Stack punches far above its capacity. It made it three quarters of the way through the 4x4 and reached the very end of the dimensional lumber cut, holding low 16s volts under load.

Compared directly, it outperformed the standard 2Ah, matched or beat the 3Ah compact, and finished cuts the 3Ah could not. Even against the full-size 5Ah XR, this tiny pack showed more grunt. For light-duty tools and users who prioritize weight, it is a genuinely impressive little battery.

The Heavyweight: 9Ah FlexVolt

The new-style 9Ah FlexVolt showed the highest resting voltage of any battery in the test, sitting at 21 volts before the cut even began. Through the 4x4 it made it all the way through with tons of power to spare, and in dimensional lumber it held mid-to-high 18s volts, the strongest sag numbers of the day.

In power delivery it behaved very similarly to the 5Ah Power Stack, and one tester described it as the closest match seen so far. The difference is capacity: with 9Ah on tap, it will keep going far longer on demanding jobs. It is simply a larger, heavier pack, which is the price you pay for the runtime.

The Runner That Struggled: 5Ah XR

The standard 5Ah XR had a rough outing. It bogged down early in the 4x4, needed a second attempt, and still only reached about three quarters of the cut. In dimensional lumber it cut out with voltage in the low 14s and could not finish, even with extra attempts and a knot-free section of wood.

It still has a place for users who value its familiar size and runtime over peak power delivery, but in a power-output comparison like this one it finished well behind the Power Stack packs and the FlexVolt.

Buying Advice: Which Battery Fits Your Work

If raw power in a compact, lightweight package is the goal, the 5Ah Power Stack is the standout. If weight matters most and your tasks are lighter, the 1.7Ah Power Stack is a remarkable small pack that beats bigger standard batteries. For long runtime with power close to the Power Stack, the 9Ah FlexVolt is the workhorse choice. The 5Ah XR remains a solid general-purpose pack, but this test showed it is not the pick when maximum power delivery matters.

A note on the test method: voltage sag depends on the tool and the material, and knots in lumber can affect results. Further testing with more tools, heat buildup, and hot-environment durability is a sensible next step before drawing final long-term conclusions.

Conclusion

The Power Stack line has genuinely shifted expectations for compact batteries. The 5Ah Power Stack delivers power output on par with a much larger FlexVolt pack in a far smaller body, the 1.7Ah version embarrasses standard compacts, and the 9Ah FlexVolt pairs that power with serious runtime. The 5Ah XR, meanwhile, is best treated as a capacity pick rather than a power pick. Choose based on whether your priority is size, weight, or runtime.