They aren't the only ones. This is very common with LiIon batteries.
Assume 4V/cell. They charge at about 4.1-4.2V and discharge down to
about 3.6V. 5x4.1V~ V. 5x3.6V~V. Pick your poison. You can't
have half a cell, so 18V and 20V batteries *must* be the same thing.
In fact, I have a bunch of 12V Bosch batteries. The older ones say
10.8V and the newer ones, 12V. Other than the label, they're
All the arguments about battery pack voltages aside, higher voltage can
be used to produce more torque. Motors have windings which all have some
amount of resistance. This resistance results in a voltage drop and with
a higher available voltage, the percentage of 'wasted' power due to the
voltage drop is less. Motor torque is proportional to current. A higher
voltage also lets you increase the available motor current and/or allows
for more windings in the motor.
One early example of this 'voltage war' is people who upgrade old VW bug
6 Volt electrical systems to 12 Volt. The starter motors are a lot more
peppy with more available current.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.