Mod Coast headlight to use 1x18650?


I’ve had this Coast HL5 headlight for years:

and just ordered a couple more from the deal that asval posted (Coast HL5 175 Lumen $8 (Home Depot)), and I really like it.

I use AAA Eneloops with this, mostly when working on flashlights (ironic, huh :)?), but they don’t seem to last very long, so I’ve tried and compared it to several newer ones I’ve bought from various places like FT and Tmart, but, the thing that I really dislike all of them, mainly because of their beams.

So, I’m wondering if it’d be possible to mod this Coast headlight to use a single 18650 instead?

I rarely use it outdoors, so water-resistance wouldn’t be an issue, so I’m thinking if I replace the 3xAAA battery holder with a 1x18650 battery box, would that work?

Has anyone done something like that?

Also, if that’d work, any ideas about how to attach it to the headband in place of the current 3xAAA battery holder?



I’ve come up with a “plan” for a kind of hack: I ordered some AAA dummy cells and a 3xAA battery box, so I’m going to try to mod one of the dummy cells and connect the wires from the battery box to the +/- leads on the dummy cell. Then, I put that modded dummy AAA cell, along with 2 more unmodded dummy cells into the original 3xAAA carrier. If that works, I’ll just glue the 3xAA battery box to the back of the original 3xAAA battery carrier, then I think I should be able to run the headlight off of 3xAA instead of 3xAAA.

I have a bunch of 3xAA Eneloops, with much higher capacity that the 3xAAA Eneloops :)…

Edit: Hmm. I actually bought 4 of the dummies, so I could also mod the 4th one to hook to an 1x18650 battery box when I find one, and then I could use either 1x18650 or 3xAAA?

Here is my custom headlamp it’s a Small Sun ZY-1801A it takes standard P-60 drop ins and a regular 18650 battery. I have a stepped 5 mode 3c tint drop in with a Trustfire 18650 in it. I use it almost daily. It does get hot on turbo mode at 3.5amps but will run at 1.8 amps all day without overheating. The candle mode is also very useful when trying to find stuff in the bedroom when the wife is sleeping. I ditched the 3AAA battery holder and used a 501B for the battery holder and a couple Ultrafire headlamp holders from KD for the headbands.


If some of you bought these HD5 headlamps on sale, here’s a very simple “mod”… no cutting, no soldering, just “plug-and-play”…

I bought 4 dummy AAA batteries:\_trksid=p3984.m1439.l2649

Shipping was pretty fast, but no tracking #. Just received them today.

So, I put 2 of those in the HD5 battery compartment, and 1x10440, and voila, there was light. I actually think that it’s brighter than it was on 3xAAA NIMH or 3xAAA Eneloops (the Eneloops were running really fast).

Anyway, that’s the “first” mod.

My longer term plan is to try to either:

1) Mod one of the AAA dummies to have some leads for +/- and hook it up to a 3xAA battery box, then use 2 of the AAA dummies plus the modded dummy, hooked up to a 3xAA battery box, or

2) Replace the original 3xAAA battery compartment with a 3xAA battery box (still waiting for some to arrive).

that’s really neat e1320, looks very professional.

the way I modded mine was to glue a single 18650 holder to the back of the 3xAAA battery box, run some wires through a couple of small holes and solder them direct to the battery springs. Worked great for a couple of years and I gave it to a friend a little while ago. Doesn’t look pro at all, but it only cost ~$2 to do :slight_smile:


Can you provide a link for the “Ultrafire headlamp holders” that you mentioned? Also, how did you get the cable/wire out from the 501B to the outside?


Ok, I’ve made some progress.

Where I am with this is that I decided that first thing, I want a way to hook up any battery into the existing headlamp 3xAAA battery pack, without having to modify the headlamp. This way, I could move my mod to any 3xAAA headlamp.

So, I’ve made a crude “fake AAA battery extender” out of a small piece of wood, and to add the contacts, I used pieces of stripped and tinned wire:

To make that thing, I chopped up one of my wife’s largish chopsticks, so mine is bamboo, but any appropriately sized dowel can be used.

To make the contacts, for the positive end, I:

  • Drilled a hole across the diameter of the “battery”, about 1/2” from the “front”
  • Drilled another hole from the front, so that this hole met the diameter-wise hole
  • Put a piece of tinned wire through the diameter-wise hole
  • Looped a piece of tinned wire, where the “tail” was long enough to reach the wire that was going through the diameter-wise hole
  • Shoved the “tail” of the looped wire down the front hole
  • Shoved some solder wire down the same hole
  • Using a soldering iron, heated up the diameter-wise wire

Heating the diameter-wise wire melted the solder wire that I’d shoved down the hole, so that created a joint between the diameter-wise wire and the looped wire (which was coming out the front)

I ohmed the wires, to make sure I had good conductivitity.

Then, I heated up the looped part of the wire, and melted some solder on it until it looked like the “nipple” on a normal battery.

For the back/negative contact, I did the same thing, but instead of making a nipple-type contact, it was more of a flat type contact to contact the negative spring.

After all of that, I had something that looked like a AAA battery, but with two wires coming out the side:

Comparing a dummy AAA battery to my fake AAA battery extender:

I ohmed all the contacts out, and after confirming that all was good, I tried it in one of the headlamps I have that normally takes 3xAAA by putting two dummy AAA batteries, plus my dummy AAA battery in it.

I then hooked up an 18650 battery to the fake battery “contacts”, and fired things up, and there was light - very bright light actually:

So, next I have to decide what to hook up to my fake AAA battery extender, then I’ll be done.

I have a bunch of 3xAA battery enclosures, but I’m still trying to find either a 1xAA or 1x18650 enclosure, because, while I could use the 3xAA enclosure with 1x14500 and 2 dummy AA batteries, I’d need to waste 2 dummy batteries.

Hey… How has your coast headlamp held up with the added Voltage?

I would like to do a similar mod but am waiting for a reply from a Coast engineer to see if the HL27 can handle the extra Volts… If yours can handle it im sure the HL27 can

Re read the post. He’s not adding voltage. That would be an instant no no. Actually he is decreasing it by a third of a volt. 3 x 1.5v = 4.5v. (technically he was using Eneloops which are typical at 1.2v x 3 = 3.6v) The Li-Ion he is now using is at it’s max 4.2v. The cells in the picture are dummy cells. They are there only to complete the circuit, they hold no voltage.