What about the voltage of the LED flashlight?
A resistor uses an electric current to decrease the current. You can't look at the voltage, mainly the current
High current LED, it is best to use a dedicated LED constant current IC, Buck type, but also step-up type, you can find it.
That resistor is the current limiting resistor,
The DCDC constant current source conversion efficiency will be better than the efficiency of a high voltage resistance, because you use a new battery when the 4 batteries will be 6.4V, then you will drop on the resistance of about 3V, power multiplied by the current on your LED is consumed by the resistance efficiency; constant current source there are usually 90%. Constant current power supply is recommended
