I had a flashlight containing 4 leds.
It worked on four button cells of 1 volt each.
Each white led can take upto 3 volts. So 4 leds could take upto 12 volts.
I decided to remove the four button cells and add a 9 volt battery to the flashlight.
So i soldered a battery cap to the four leds.
(Black wire of the battery cap to the negative of the LED and red wire to the positive of the LED assembly. )
Final result was a powerful flashlight!
Potential 12 volt leds, earlier running on 4 volts, now running on 9 volts!
This conversion can be done on any flashlight with more than 3 LEDs.
Happy with the outcome! ;-)