Voltage is the same, it's about amp hours and amp draw. You can make big power with low voltage (as demonstrated by vehicle starters) but amps skyrocket....something about some guy named Ohm writing a lawThe big Milwaukee tools work fine if you use the high output batteries on them. They figured out that you can’t use the 18650 based batteries with the big stuff and get long operation. That is why the low voltage tools got such a bad name in the beginning. The voltage has to be high to get the time out of those smaller cells.

I remember reading the battery powered manufacturers were dealing with potential spikes of 400A or more on these new "high draw" 18V tools, which obviously begins to present some problems with wires and conductors
Either way I really like my Milwaukee 18V string trimmer but we don't get crazy high or wet grass here in the Southwest.