DeWalt Battery Voltage Comparison: Which Battery Delivers the Most Power in Small Tools?

Introduction

DeWalt’s battery lineup has grown crowded: Compact packs, XR packs, FlexVolt, and now the 5Ah PowerStack. On paper they differ mainly in amp hours, but in a small tool the story is very different. To find out which battery actually delivers the most usable power, we ran the full range through a DeWalt Atomic impact driver, driving screws into wood while measuring the voltage each pack delivered under load.

The logic is simple: voltage sag under load shows how much power the tool is actually getting. A bigger pack that holds its voltage higher gives more performance, not just more runtime. The results were revealing, and they changed which battery we would pick for small tools like this driver.

How the Test Worked

Each battery was fitted with test wires tapping its output so voltage could be monitored live while the Atomic impact driver drove lag screws into wood. We watched how far each pack’s voltage dipped as the tool worked. This reflects the cells inside rather than just the label on the pack, but we refer to each battery by its amp hour rating and designated name.

The spread of packs tested covered the 2Ah Compact, the 1.7Ah PowerStack, the 3Ah and 4Ah Compacts, the 5Ah XR, the 5Ah PowerStack, the 6Ah 20V, the 8Ah XR 20V, and the 9Ah FlexVolt.

Why Voltage Drop Matters More Than Amp Hours

The small packs showed the widest range. The 2Ah Compact consistently dropped to around 16 volts by the end of a screw, the lowest reading of the group. The 1.7Ah PowerStack held in the mid-17s, giving a noticeable step up in power despite its smaller rated capacity.

The 3Ah Compact held high-17s to low-18s, and the 4Ah Compact landed in a similar zone, with readings around 17.6 volts as a low. Moving up to the 5Ah XR brought readings in the high-17s and low-18s, decent numbers for a pack many people reach for by default.

The 5Ah PowerStack was the standout. It stayed in the 18-volt range throughout the test, never sagging as low as the packs below it. Combined with its footprint, which matches other DeWalt batteries built on 21700 cells and is not as tall as the 6Ah pack, it looks like the right size for a tool like this driver: strong power delivery without excess weight.

High-Capacity Packs: When Big Batteries Make Sense

The 6Ah 20V never got into the 18-volt range in this test, which feels like overkill on a tool this small. Interestingly, the 8Ah XR 20V did reach the 18s, consistent with it outperforming the 6Ah pack in other applications as well.

The 9Ah FlexVolt, a battery you would never normally pair with a compact impact driver, delivered mid-to-high 19 volts, the strongest and most stable readings of the day. That confirms what the numbers suggest: more cells and more capacity translate directly into higher sustained voltage, but at a cost in size and weight that makes little sense for a small driver. For decking or long-duration jobs where you do not want to swap packs, a larger pack can still earn its place.

A 5Ah PowerStack battery is also set to ship with an upcoming kit that includes a 7 1/4-inch circular saw, and the same battery might really shine in that application. We plan to run the same test on that saw once we confirm the kit version matches the one currently available.

Overall Buying Advice

Here is how the results stack up for an Atomic impact driver:

Battery	Voltage under load	Takeaway
2Ah Compact	Down to ~16V	Lightest, weakest power
1.7Ah PowerStack	Mid-17s	More power in a smaller pack
3Ah Compact	High-17s to low-18s	Solid step up
4Ah Compact	~17.6V low	Similar to 3Ah
5Ah XR	High-17s to low-18s	Decent all-rounder
5Ah PowerStack	Held in the 18s	Best balance of power and size
6Ah 20V	Never reached the 18s	Overkill for small tools
8Ah XR 20V	Reached the 18s	Outperforms the 6Ah
9Ah FlexVolt	Mid-to-high 19s	Maximum power, maximum bulk

For most people, the 4Ah range is where they will land, and there is not much difference in footprint between that and the PowerStack. But given the PowerStack’s performance and lighter weight, it is our pick if power in a relatively compact pack is the priority. If you need long runtime for decking or extended jobs, the larger packs make sense, though the 8Ah XR looks like the stronger choice among the big 20V packs.

Conclusion

The clear pattern in this test is that the 5Ah PowerStack gives an Atomic impact driver everything it needs: power delivery in the 18-volt range with a footprint similar to other mid-size packs. Smaller Compacts trade power for lightness, while FlexVolt packs deliver the highest voltage but are impractical on a tool this small. Match the battery to the job, and you will get the best of both power and runtime.