18V vs 20V MAX: Is There Actually a Difference?
No. Both describe the same 5-cell lithium-ion pack. 20V MAX is the no-load peak measured fresh off the charger; 18V is the nominal voltage under an actual working load.
"20V MAX" is a peak, no-load marketing number — the same 5-cell lithium-ion pack is 18V nominal under an actual working load. DeWalt states this directly on its own spec sheets: 20V is measured fresh off the charger with no load; 18V is what the tool sees once you pull the trigger under real work. Milwaukee's M18, Makita's 18V LXT, and most rivals report the more honest nominal number directly, which is why a DeWalt 20V MAX tool and an 18V-labeled competitor are actually the same voltage class.