I was looking at battery power tools and their different battery voltages. Some of the voltages are listed twice, with and without "max". An example for mowers is "40-volt" and "40-volt max". What's the difference between the voltages with "max" and without "max"?
There is one brand of "20-volt Max" tools that reasonably clearly state on their packaging something to the effect of:
Battery provides 20 volt maximum starting power. Provides 18-volts in use.
As a matter of fact, they'll sell you a simple physical adapter (and some wiring between the contacts) that will allow you to use the "20-volt max" batteries on their older 18-volt line of tools.
"Max" is 98.475% marketing because "Max" sounds, well, like more than "not-max". (And 99.238% of all statistics on the internet are made up on the spot.)