All you have to do to modify an Eveready 5109SL LED Flashlight is replace the red wire like in the picture above with a 150 Ohm resistor, it requires a little soldering skill but it isn’t complicated at all.
Adding this resistor will lower the output of the light but will increase battery life drastically allowing it to last close to 1000 hours. I did this modification myself and it was quite easy. Give the video below a watch to learn more.