We are going to take a long run time flashlight (65 hours) and turn it into a longer run time flashlight (Update: The title of this Instructable says 3.6x run time but actual run time ended up being over 360 hours with a zinc carbon battery. That would be over 600 hours with an alkaline battery).

Yes it is another long run time flashlight hack. This one is easier than my other one. All you need a resistor, a soldering iron and this flashlight.

This Eveready flashlight model number 5109LSH15 (old model number 5109LSH7 or 5109LS) costs under $5 if you shop around. This is a great long run time flashlight to have even if you don’t do the modification.

Where to buy:


I like this flashlight because as is it has a long run time before the battery needs to be replaced. It is bright. It is cheap and it is easy to hack. You can do this hack in 10 or 15 minutes and most of that time will be waiting for your soldering iron to heat up.

The only thing about this flashlight that is less than optimum is that the 3 LEDS (original design. the new design has one high power LED) have a little too much current going through them. The LEDS appear to be “straw hat” type (20 milliamp) LEDS. Each LED has about 60 milliamps running through it.

Note: See the last step for the modification for the current version of this flashlight.

Here is a data sheet for a straw hat LED:


The LEDS in this flashlight may be specially made to handle more current but in case they are not, this modification will bring the current down to a level that will insure tens of thousands of hours of LED life.

I chose to add a 56 ohm resistor to the circuit so each LED runs at about 16.5 milliamps. This will increase the run time by 3.6 times.

The other step by step instructable to make a long run time flashlight is here:


Either one will be good to have in an extended power outage.

Step 1: Un-solder

You will need to unscrew the black ring that hold the clear plastic cover on the front of the flashlight. Then remove the assembly shown in the picture above. Install the battery and re-assemble the flashlight. Test the flashlight to make sure it works. Remove the rind and assembly shown in the picture above. Un-solder one of the two red wires from it’s metal contact. I chose the one on the left.

<p>Modern LED flashlights already have an IC that can let you select between low/high power setting or low/med/high and even extra options like SOS.</p>
<p>I made this modification out of Ron Brown's e-book (in which you are mentioned, luxstar), but unknowingly picked up one of each kind of flashlight when I was at Lowe's. Thanks for putting up a version of the mod for the new style!</p>
<p>Thank you Dreadalus</p>
Ok, what did I do wrong. I did this with a 47ohm resistor and I can barely see the light. New battery and new flashlight, but it's really dim.
I am not sure what went wrong. I have modified over 10 of them and clubmike and mkia did it too without problems. I have two thoughts. Did you tests your flashlight before you did the modification and it worked fine then? Maybe you actually are using a 470 ohm or a 4.7k ohm or a 47k ohm by mistake. You may want to check it with an ohm meter. <br> <br>Good luck
Day 131 still on but not enough useful light. 3144 hours on time. Bummer, I feel lost not carrying my light with me. Time for new battery.
131 days is quite impressive and useful. <br> <br>I am re-charging my original 6 volt alkaline with 3 of the cheap walmart solar lawn lights in series. I took out the circuit board, batteries and LEDS and wired them in series and put them on the roof and ran cat5 cable down to the garage. Also I have a blocking diode in the circuit. I am up to 5.82 volts. If I can get up to about 6.2 volts I will run one of the tests over again.
Another update on your forever flashlight. Test started on 3/1/13 at 3:10 pm. <br>First update on 5/27/13 on 87 days{2088hrs}. 7/7/13 at 3:10 pm flashlight will have been on for 128 days{3072hrs}!!! <br>Still used for a nightlight, finding car door, house key locks etc. <br>First major drop in brightness was after being on for 14 days{336hrs}. <br>Since then it has been dropping gradually. Thank you.
Thank You MKIA.
Ok i'm going to give this a shot i have to get some batteries but i have some of these flashlights laying about can't hurt to give it a shot thanks for this great idea you made it easy for me to understand and teach to my kids too .....
Let us know how it goes.
Why not put the resistor in the other wire (to the positive terminal?)
Either side will work. Take your pick
Cool. I like those flashlights. The old kind with the maglite bulbs eat batteries, and the Nite Ize maglite LED bulbs don't work in them because of polarity. The ones you show (come with 3 LED) are pretty good, but I recommend gorilla taping the ring cap if you put it on a bike handlebar or something. I used one to mow my yard at dusk when it's cooler.
Thanks for showing me the light!! All I could get was a 42 ohm resistor. It has worked fantastic. Turned mine on on 3/1/2013. Today 5/27/2013 at 3:10pm it will have been on for 87 days straight{2088 hours}. Still has a usable light, unlocking doors, reading if you want to.
Thanks for the feedback MKIA. It is good to hear that people are actually trying this.
ok, I did this, it worked great in fact it is still working. I soldered a 100 ohm resistor in the flashlight on Feb 5 and turned on the flashlight. It is still on and it is March 30. I can still read my calender with it and see down my back stairs to let my dog out at night. In an emergency situation this is exactly what I need. The question is how long will it last?????
Thank You Clubmike. <br> <br>When your battery finally does run down you can more than double the run time by replacing the junky carbon battery that came with the flashlight with an alkaline.

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