Maglite 18650 Battery Conversion

maglite 18650

Maglite’s used(?) to be the king of flashlights, but replacing those pesky D-cell batteries is kind of ridiculous in this day and age. So [Travis] decided to upgrade it to make use of the ever-so-common, 18650 lithium-ion battery.

Not looking to purchase any components [Travis] performed this hack using simple recycled household parts. You could solder tabs on the 18650’s so they better mimic a typical alkaline battery cell, but [Travis] notes that because most solder tarnishes the electrical conductivity isn’t always the greatest. So instead, he used aluminum foil. It doesn’t look professional, but it does the job and keeps all the components unmodified so the lithium cells can be used elsewhere if needed. To center the batteries inside the Maglite he used a few strips of cardboard from a case of beer — again, this is just making use of what was available. That being said however, if you wanted to do a professional job on it, nothing is stopping you! A 3D printed 18650 to D-cell adapter would look quite nice… Finally, in order to make the battery spring contact the smaller surface area of the lithium cells, all you have to do is flip it around backwards and slightly bend the inner spring out. That’s about it.

It’s a pretty simple hack we admit, but definitely super handy. In a past project [Travis] also replaced the halogen bulb with a high power LED, making this flashlight even more powerful — and because the LED driver accepts a broader range of voltages it lasts longer too. If you need more inspiration for retrofitting flashlights with LEDs check out this switch-mode driver board hack.

Unfortunately this hack does reduce the Maglite’s thief-head-bashing-ability with such light batteries.

30 thoughts on “Maglite 18650 Battery Conversion

  1. Even without wanting the option of using the Maglite as a weapon (which I definitely /do/ want), there’s something satisfying about the sheer heft of a 4-cell Maglite. I guess you could always make the battery holder out of milled or printed metal instead of cardboard or printed plastic. There’s at least one 3D printing service online that will print in a lot of different materials, including metals.

    Or you could just salvage some rebar or some such and try to fit that in there…

      1. +1 LEDs but for weight pour some lead weights to fill on the gaps around where the wires/li-po batts would go. The heatsinks for the LEDs could be (crennalated?) to act like a mace for additional offensive capabilities. Metal of choice would be steel but for thermal condutivity aluminum would be best but not as strong. Anyone know if titanium is good for heatsinks?

        1. Decent amount of space in there if I’m only using 3-4 lithium cells… Could machine a nice bar of steel to hold the batteries in place. Bigger question is cooling the heatsink though…

          1. I’m sitting here looking at Sure-Electronics, DX, Eachmall, Banggood, etc., trying to find a premade 2-D-Cell and LED bulb replacement. Does that make me a bad person or bad, lazy person? :P

      1. If you don’t want to use a Maglite, there’s always those 6V lantern battery-powered ones. They would actually be ideal with the flat cells. You’d even have room to install the charger circuit. I have both the “AA” and (various sizes of) flat cells so I could try both.

        I actually found this article while looking to see if anyone sold adapters to put a lithium cell in the place of 2 D-cells. A battery pack with 2 18650’s in parallel would seem to be almost perfect for older flashlights, regardless of it they’re Maglites. I already have an 18650 charger.

  2. Why wrap shit around 18650 cells when you can get 32600 (same size as a “D”) with about 2x the capacity??

    Also, you should NEVER solder anything to lithium cells, you’ll only destroy it that way…(might even cause a thermal runaway)
    The proper way is spot welding nickel tabs ;-)

    1. You know what… since this is a hacker site, and the best hacks are elegantly simple on the level of the Wozniak drive controller logic, here’s my suggested project:
      1) Get a 32xxx lithium cell (longer is better but no more than 2 D-cells).
      2) Get some waste lead from your solder barrel. I mean, everyone has a barrel full of their soldering tips and old solder, right?
      3) Make a block the same length as what’s needed to make the lithium cell reach both terminals. Ideally a cylinder, for maximum weight. It needs a tiny spring embedded or you can do optional step 4 for extra cheapness.
      4) Pull out the spring and place the block behind the spring after putting the lithium cell in the flashlight.

      If I actually tried this, I’d probably find that a small tab/spring is the preferred option. There seems to be no need to insulate the metal block as it’s just going to ground out to the same metal frame that’s the ground plane. I would NOT recommend trying to put it on the positive side of the cell.

      An alternative: Take an existing (discharged) D-cell and solder wires across the terminals. Great if you’re using 32650’s.

      Recycling dangerous lead into an even more dangerous flashlight is funny? Just don’t try and sell this as ROHS. Of course, define hobby versus a job… Seriously though, sequestering the lead is the only safe way to keep it out of the environment. It’s not like it’ll magically turn into iron or silicon or something. BTW: I love that bismuth stuff – it makes SMD a lot less difficult.

  3. Much like the numerous AA-to-D cell adaptors out there, it looks like there’s an opportunity for someone to create some 18650-to-D cell adaptors, with appropriate bulb to handle the increased voltage.

    1. Hell, if you have a 6V bulb in a 3V flashlight, then you don’t even need any ‘adapters’ except maybe stretching a spring. I’m wondering when a professionally done adapter with voltage conversion between 2 lithium cells and a 6V bulb will become common. Sadly, voltage step-up/down converters tend to be unideal at ratios like 5:4. They’re more intended for 2:1 or higher.

  4. what’s wrong with D cells?

    Back in the day, I worked in a gun shop, we used to put 2 cell bulbs in 4 cell maglites, then had our gunsmith turn up some D cell sized brass spacers.

    1. Theoretically, that works great. The practical problem with that is manufacturing the spacers. It’s not exactly cheap, and it’s not exactly easy to do at home, seeing as how having a lathe that can handle the brass cylinders and the knowledge and experience to use it comes at quite a cost of both money and time.

      Though, I have to say, if I were to do it myself, and I had the means, I’d probably make a large cylinder out of brass into which the batteries fit, with special end caps for the proper contact between the battery and the respective positive/negative terminals on the flashlight. That would give heft, stability, and the warm, fuzzy feeling of a job well done.

      1. it was done for the, umm, “hurt” factor.

        One of the security guards at the Adelaide Botanic Gardens got the shit kicked out of him by some pricks wanting to know “where the grass was”.

        my gunsmith managed to get brass stock that was pretty close, he just put the + end “nipple” on.

      1. And are actually against many city’s policies? Hey, if you’re going to kill someone, use a gun. If you’re going to restrain someone, use a side-handle baton and really strong arms. I’m curious how many prefer a lighter baton for speed or a flashlight/club for power. My mom is a security guard and uses a black 2-cell Maglite because it’s all she owns and they’re cheap. :/

  5. How about a newbie question. I’m playing with an old MiniMaglite 2XAA. Upgrading to a 150 lumen LED. What would happen if I tried substituting Li-ion batts (14500) in place of the AA? Anyone know if the LED can take the higher voltage? Will it glow or blow?

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