Short answer: a DeWalt 20V MAX battery and a Milwaukee M18 battery are the same thing electrically. Both are five lithium-ion cells in series. DeWalt rates the pack by its maximum initial voltage off the charger; everyone else rates the same pack by its nominal voltage. Nobody is exaggerating and nobody is lying, but only one convention is used consistently, and it is not DeWalt's.
DeWalt states this itself. That is the asterisk in "20V MAX*".
DeWalt's Own Footnote
From DeWalt's published product specification for the 20V MAX system:
Maximum initial battery voltage (measured without a workload) is 20 volts, and nominal voltage is 18.
Two numbers, one pack. 20 volts is what a meter reads across a fully charged battery sitting on the bench with nothing connected. 18 volts is what the pack actually holds under load across most of its discharge. The second number is the one that describes the tool you are using.
Why Five Cells Produce Both Numbers
A standard lithium-ion cell is rated at 3.6 volts nominal and reaches roughly 4.0 to 4.2 volts at full charge. Put five in series and the arithmetic is unavoidable:
| Measure | Per cell | Five cells in series | Marketed as |
|---|---|---|---|
| Nominal (under load, most of the discharge) | 3.6 V | 18 V | M18, 18V LXT, 18V ONE+, Bosch 18V |
| Maximum initial (full charge, no load) | 4.0 V | 20 V | 20V MAX |
The same physics scales up. A 10-cell pack is 36 V nominal and 40 V maximum initial, which is why you will see both numbers used for what is functionally one class of battery.
The Platforms, Normalised
| Platform | Marketed voltage | Nominal voltage | Cells in series | Convention used |
|---|---|---|---|---|
| DeWalt 20V MAX | 20 V | 18 V | 5 | Maximum initial |
| Milwaukee M18 | 18 V | 18 V | 5 | Nominal |
| Makita 18V LXT | 18 V | 18 V | 5 | Nominal |
| Ryobi 18V ONE+ | 18 V | 18 V | 5 | Nominal |
| Bosch 18V | 18 V | 18 V | 5 | Nominal |
| Metabo HPT 18V | 18 V | 18 V | 5 | Nominal |
Five of six platforms use the same convention. DeWalt uses the other one. That is the entire source of the confusion, and it is a labelling difference rather than a hardware one.
So a 20V Tool Is Not More Powerful Than an 18V Tool
Not because of the voltage number, no. If you are comparing a DeWalt 20V MAX drill against a Milwaukee M18 drill, the voltage on the label tells you nothing at all — you are comparing 18 V against 18 V and one of them is wearing a different sticker.
Real differences between two tools on the same nominal voltage come from somewhere else entirely:
- Amp-hours (Ah) on the pack you actually own. This is capacity, not power — it sets runtime. A 2.0 Ah and an 8.0 Ah pack on the same platform deliver the same voltage and very different working days. High-capacity packs also sag less under heavy load, which shows up as sustained performance in dense material.
- Brushless versus brushed motor. A far bigger determinant of output and efficiency than any voltage label.
- The tool's own gearing, electronics and thermal design. Two drills on identical packs can differ substantially in torque and in how long they hold it.
- Platform breadth — how many tools you can eventually run on the battery you are buying into.
Where Voltage Genuinely Does Matter
Across classes, not within them. A 36 V or 40 V nominal platform (10 cells) really does deliver more than an 18 V one, which is why higher-demand outdoor equipment and larger saws live there. The comparison that means something is 18 V against 36 V. The comparison that means nothing is 18 V against 20V MAX.
One Practical Trap: DeWalt's Own Two Platforms
DeWalt sells a DCA1820 18V to 20V adapter, which exists because DeWalt's legacy 18V line and its 20V MAX line are genuinely different platforms with incompatible physical connections. So within DeWalt, "18V" and "20V MAX" are not interchangeable names for one thing — they are two separate battery systems.
This is the opposite of the cross-brand situation and it catches people out. Across brands, 18V and 20V MAX describe the same electrical pack. Inside DeWalt's catalogue, they are two incompatible product lines.
Frequently Asked Questions
Is 20V more powerful than 18V?
No. DeWalt's own specification states that a 20V MAX pack has a nominal voltage of 18. Both are five lithium-ion cells in series. The 20 V figure is the maximum initial voltage measured off the charger with no load; the 18 V figure is the working voltage. Compare amp-hours, motor type and tool design instead.
Why does DeWalt say 20V MAX when others say 18V?
DeWalt rates the pack by its maximum initial voltage rather than its nominal voltage. Milwaukee, Makita, Ryobi, Bosch and Metabo HPT all use the nominal figure for the same five-cell architecture. It is a labelling convention, not a hardware difference, and DeWalt discloses the nominal number in its own published specifications.
Can I use a 20V MAX battery in an 18V tool?
Not across brands — every platform uses its own physical connection, and batteries are not interchangeable between manufacturers. Within DeWalt specifically, the legacy 18V line and the 20V MAX line are separate platforms; DeWalt sells the DCA1820 adapter precisely because they do not fit each other natively.
What should I compare instead of voltage?
Amp-hours on the packs included in the kit, whether the motor is brushless, how many tools exist on the platform you are buying into, and the battery warranty — which never exceeds three years at any major brand.
Does a higher-voltage platform ever actually matter?
Yes, across classes. A 36 V or 40 V nominal platform uses ten cells rather than five and genuinely delivers more. The meaningless comparison is 18 V against 20V MAX; the meaningful one is 18 V against 36 V.
The Buying Consequence
If voltage is doing none of the work, the decision is a platform decision: which battery system you want to be buying into for the next several years, and what it costs to stay there. Our comparison of 7 cordless combo kits covers what each includes and how far each platform extends.
Worth reading alongside it: our comparison of what those platforms actually warranty. No brand covers a battery for more than three years, and the brand advertising a Lifetime tool warranty covers its batteries for two.
Sources and Limits
The DeWalt nominal-voltage statement was read from DeWalt's published 20V MAX system specification on 2026-08-24, as was the existence of the DCA1820 18V to 20V adapter. Platform names and their marketed voltages were taken from each manufacturer's own product pages on the same date.
Limits. Cell-level nominal and maximum figures (3.6 V and roughly 4.0 to 4.2 V) are standard lithium-ion characteristics rather than a per-brand published specification, and individual cell chemistries vary slightly at the top of the charge. The five-cells-in-series architecture is inferred from the voltage arithmetic and is consistent across every 18 V and 20V MAX platform listed, but manufacturers do not universally publish internal cell counts. Nothing on this page is based on physical use of a tool or on opening a battery pack.
