More voltage puts more current in faster. What's really important is the delta peak.
Anyway your battery is what drives your gun. If your battery dies, your gun won't run on wishful thoughts or hope. The life of your battery depends entirely on how much money you spent on your charger.
So you can have a crap charger, and you battery can be at 60% performance all the time, which means your gun is at 60% performance all the time. Or you can get a good smart charger and have your batteries at 100% all the time.