4 or 5 watts is NOT really low. Check out this calculator here: http://www.rapidtables.com/calc/electric/watt-volt-amp-calculator.htm
The brass knuckles adjustable pen adjusts from 3.2 - 5 volts, and has a 680 milliamp battery. 4 volts is pretty hot, and at 4 volts, you're still pushing under 3...