Is a 20V battery more powerful than an 18V one?

This is the most successful piece of marketing in the power tool aisle. Two identical packs sit side by side labelled 18V and 20V max, and the larger number sells. Understanding what is being measured takes two minutes and stops you paying a premium for arithmetic.

Step by step

1. Understand how a lithium pack is built.Cells are wired in series. Each lithium-ion cell has a nominal voltage of about 3.6 or 3.7 volts and a fully charged voltage of about 4.2 volts. Five in series gives a nominal 18V and a fully charged 20V.
2. Recognise the two conventions.European and most trade brands quote nominal voltage — 18V. Several brands, particularly in North American marketing, quote maximum charged voltage — 20V max. The pack is identical.
3. Note that the peak lasts moments.A pack sits at its charged voltage only until you pull the trigger. Under load it drops to around the nominal figure almost immediately, which is exactly why nominal is the more honest number.
4. Apply the same logic to 12V.10.8V and 12V max describe the same three-cell pack for the same reason. Neither is more powerful than the other.
5. Know where voltage differences are real.12V against 18V is a genuine step. 18V against 36V, 54V or a paired-pack system is another. Those change what the tool can do; 18 against 20 does not.
6. Beware apparent cross-compatibility.Because the packs are electrically equivalent, people assume they will swap between brands. They will not — the mounts, the latches and the data pins are proprietary.
7. Compare on the things that vary.Amp-hours, cell quality, current delivery, weight, charger speed, warranty and the range of tools on the platform. All of those differ meaningfully between brands. The voltage label does not.

Tips

• Some brands run a flexible pack that reconfigures its cells between 18V and 54V depending on the tool. That is a genuine engineering difference and it is described as such, not as a marketing figure.
• If a listing quotes 20V without saying max, check the cell count. Five lithium cells in series is an 18V pack whatever the box says.
• Watt-hours are the only figure that lets you compare packs of genuinely different voltages fairly, and it is usually printed on the pack itself for shipping reasons.

Common mistakes

• Paying more for a 20V platform believing it is more powerful — It is the same pack described differently. The money is better spent on capacity, on a second pack or on a better tool.
• Assuming 18V and 20V packs interchange because the voltage matches — The physical mount and the electronics are brand-specific. Electrical equivalence is not compatibility.

Questions people ask