A lithium-ion cell delivers 3.6 volts in use and 4.0 volts at rest. Five cells in series therefore give 18 nominal volts or 20 volts max, depending on when you measure. Both figures describe the same battery. North America quotes the no-load figure, Europe the nominal one.
Nominal is the battery's real working voltage (3.6 V per cell). Max is the resting voltage, measured with no load (4.0 V per cell). An 18 V nominal battery and a 20 V max battery are the same battery under two names, depending on the market. It is the single biggest source of confusion in the category.
What each maker states
| Platform | Nominal voltage | No-load voltage | Cells in series |
|---|---|---|---|
| Bosch Home and Garden Power for All Alliance | 18 V | 20 V max | 4 cells |
| Bosch Professional AMPShare | 18 V | 20 V max | 4 cells |
| DeWalt 20V MAX (North America) / XR 18V (Europe) | 18 V | 20 V max | 4 cells |
| Einhell Power X-Change | 18 V | 20 V max | 4 cells |
| Makita LXT | 18 V | 20 V max | 4 cells |
| Metabo CAS (Cordless Alliance System) | 18 V | 20 V max | 4 cells |
| Milwaukee M18 | 18 V | 20 V max | 4 cells |
| Parkside (Lidl) X20V Team | 18 V | 20 V max | 4 cells |
| Ryobi ONE+ | 18 V | 20 V max | 4 cells |
Why the double convention exists
The no-load figure is more flattering, and it is accurate: a fully charged cell really does read 4.0 volts before anything is asked of it. As soon as a tool draws current, voltage settles back towards 3.6 volts per cell. Both numbers are true; they simply measure at different moments.
The problem is not the measurement, it is the comparison. A buyer reading a US review of a 20V driver and a European sheet for an 18V driver thinks they are comparing two classes. They are comparing the same product twice.
The voltage differences that are real
Real voltage gaps do exist, and they are not the ones in these numbers. A 12V platform is a separate class, built for compactness and awkward positions. A 36V or 40V platform is a separate class, built for sustained power. Between those two, everything badged 18V or 20V MAX plays at the same voltage.
What actually separates two batteries at the same voltage is capacity in amp hours, the current the cells will deliver, and how well heat is managed.
Frequently asked questions
Is a 20V MAX battery more powerful than an 18V one?
No. At the same capacity and generation they are the same cells. The difference lies in when voltage is measured, not in the energy available.
Can I put a 20V MAX battery on a tool badged 18V?
If both belong to the same platform from the same maker, yes: it is literally the same battery. If they are different brands, the answer is no, whatever number is printed on them.
Why do some makers advertise 54V or 60V MAX?
Those are switchable cell packs: they present as 18V on one tool and regroup their cells into 54V on another. Backward compatibility runs one way only, from the high voltage pack down to the lower voltage tool.