I've been helping my brother build his new house and I kinda fell in love with his flashlight. It's this one here:

Nebo Slyde King Flashlight & Work Light

I have one of my own now, and it's great. It's super bright, the magnetic base comes in handy when working on my truck or my motorcycle, and I love being able to slide open the work light, drop it in the hammer loop on a tool belt and just walk around with it.

The battery kinda blows though. I get a bit shy of 4 hours per charge out of the work light. Less if I use the main light, and it just uses a USB charger, so you can't just change out the battery... Or, can you?


Before you do anything with your flashlight, there is one gotcha. The flow controller thinks the battery is empty every time you switch it out. To get the light working again, you just have to plug it in for a second after you swap the battery out.

The end cap comes off, revealing... another end cap... which you can also twist off. Doing this, will reveal a battery. A 2Ah 3.7v 18650 battery to be specific. Only problem is, it doesn't look standard.

This one has a little PCB on top and a wire under the shrink-wrap that puts the negative terminal at the top as a ring surrounding the positive terminal.

I wanted to make something that would let me use standard 18650 batteries, so I can throw them on a charger and just swap them out when needed.

Time to get a closer look at that battery.

Peeling off that outer layer of shrink-wrap revealed that, what I thought was the top of the battery, was actually the bottom. It also looks like the little PCB in there has some components on it. I played around with just connecting batteries up to the terminals in the flashlight, and it looks like that little board acts as the battery's flow controller, ensuring the light stays nice and bright right up until it runs out of juice. Kinda makes sense, since 18650 batteries don't have their own. Weird that they didn't just put that in the flashlight itself though.

Anyway, let's make our batteries swappable by turning that into this:


It's a bit hard to tell what this is, so I'll explain, left to right. First up, we have the little board from the original battery. Next, we have the spacers that insulated that board from the battery. Then, a piece of PCB made into our positive terminal. Penultimately, there's a wire. 24-AWG, smashed flat with a hammer(I take the term DIY very seriously) and covered in some tape. Why the tape? Because this flashlight is metal. Literally.

It's not there in this picture, but I also put some tape around the top piece to keep the two wires connecting the control board from contacting the sides. Finally, on the other end of the wire is another piece of PCB made into our negative terminal. I left the copper on the back side of this one.

Now I can just slip that little guy around any 18650 battery, drop it into my flashlight, and get back to work.

Notice the tape?

Step by step

  1. Tear the wrapping off your flashlight's original battery.IMG_20171206_143530
  2. Pull the control board and its insulators up away from the battery.IMG_20171206_143936
  3. Snip the negative lead as long as you can. It's welded on, not soldered, just file or grind off the little bit left on the battery later.
  4. Peel away the paper cover over the positive terminal and snip that lead too.
  5. Prepare your terminals. I just used a dremel tool to clear away the unwanted copper. For your positive, you'll want to then drill a small hole through the board in the middle.
  6. Folding your positive lead(the long one, in case you forgot) betweeen the insulators and your home-made terminal, pull it through that hole you made, get it nice and snug, fold the wire so it's got good contact with the copper, and then put a nice blob of solder on that copper. You want that build right there to make the terminal stand out away from the board. Unless you plan to never use flat-top 18650 batteries(like the one sitting on your work table right now).IMG_20171207_153516I left the copper around the edge because I'm going to use a bit of it to connect the negative terminal to my wire to connect it down to the negative terminal.
  7. Using a flat wire, connect your negative terminalIMG_20171208_175407-1Make sure to get your wire the right length for the type of batteries you intend to use(flat-top batteries are a little shorter) and bend it right at the edges of the boards.
  8. Cover up the exposed wires and slip it over a battery, positive side towards the controller and then drop it in your flashlight.IMG_20171208_175818-1
  9. Get more batteries! I got these:
2PCS Panasonic 18650 NCR18650B Rechargeable Li-ion Battery, Flat Top 3.7V 3400mAh

I keep them on this charger in my truck:

Intelligent Charger, SEWE LCD Display Universal Smart Charger for Rechargeable Batteries Li-ion batteries 18650 18490 18350 17670 17500 16340(RCR123) 14500, Ni-MH/Ni-Cd A AA AAA Batteries

I also put one of these in there and it works perfect for this flashlight

Maglite Black Universal Mounting Brackets for C-Cell Flashlight, 2 pk