Good to see progress.
I’ve been stalled.
I took a break from working on the body and moved to the battery box.
Although the body is more interesting, the real challenge for me in this build is the battery box since it was designed for 4*AA batteries and the it is really hard to squeeze bigger 18650 cells into it.
another problem is the contacts, since I want to use 3.7V, one contact have to be placed on the lead and I have to find a way to wire this contact to the bottom part. I really have no Idea how to do it without risking with contacts or wiring problems.
Anyway, the first step was to remove all the old AA parts. Because the plastic structure is deep and none of my tolls was able to remove all the old parts and make place for 18650 I had melt the plastic at the bottom of the box using my old soldering iron (did it in a well ventilated place to avoid birthing melt plastic :) )
Original AA contacts
After melting the bottom parts
Not enough place for 4 cells
This project is up my alley! I’ve modded/retrofit l9ghts from incandescent to LED and it’s not easy so great job so far. For the batteries have you considered using 14500’s? They are not as high capacity as 18650, but you can use them in parallel for more capacity. Or just use 3 18650 unless you need series or series/parallel.
Imagine 8 × CR123As… 
(16mm, not 18mm.)
Thanks Guys.
I have chosen 18650 cells for few reasons:
First, I have tons of 18650 from old laptops so it is practically free.
But more important, in caving we always carry 2 or 3 lights for backup and spare batteries for each light. So it is easier when all lights are running the same battery size so I only have to carry one type of cells.
Single 18650 headlamps are very common and I have few so it make sense to use 18650 for this light too. It also allows me to borrow cells from friends in the cave in case I am running out of cells
It is also the reason why I chose no to use 1S2P pack that can solve a lot of problems and make the built a lot simpler.
Nice, “planning to change EVERYTHING”. Looks like an epic modification 
Building a boat, are we?
Tanks PP, everything but the host :)
We should have a Budget boats forum
A bit more progress today with the battery box today,
I decided to use only two 18650 in parallel so I will have space in the box for wiring and the cells will sit in the center of the box to keep it balanced.
Two decent capacity cells will last a whole day of caving on low (~150 lm) to medium (~300 lm) brightness with short periods of Turbo (~1000lm).
Placing the springs at the bottom of the box (and not on the lid) will pop the cells out so I guess it will be easier to changes cells.
First step was to create a template for the lower board
Than to copy it to the Prefboard (on the right is the prototype :) )
And cut and solder springs
I know that many BLF members are bypassing the spring but since my "Turbo" is only 2.8A, I decided not to use bypass.
Next step is it the wiring, I have some Ideas how to connect the contacts on the lid but still not sure what is the best way
And if that 2.8 amps is supplied by two cells in parallel it is only 1.4 amps per cell. IMO, you don’t need to bypass the springs.
Exactly what I am thinking :)
Didn't have a lot of time today so I only made a small progress with the battery box wiring.
I decide to use screws terminals (not sure if it the correct English term, in my language we called it chocolate connectors since it looks like chocolate table :) ) for the wire connecting the battery box to the lamp.
The reason I prefer screws over soldering is that most caving lamp issues are related to the cable and using screw will allow some troubleshooting "on the field".
The black wire is for the negative pole on the lid but this will be explained on the next update...
As promised, today I made the wiring from the power cable to the lid.
I considered many option and the two best option IMO were:
1. A dummy cell to conduct between the bottom board and the lid.
2. A wire (with or without connector)
I decided not to use a wire since I am afraid that frequent battery changes may cause contacts issues along the cable or at the soldering points and as a primary caving lamp I need to be super reliable.
For the "dummy" cell I used an old piece of Polypropylene I have from another project
I cut and sand it to fit inside the battery box with a small groove for the 18650 on the other side.
The top part had to be smaller to allow closing the lid
After a lot of hand-sanding it fits perfectly :)
You can also see the drill for the wire at the center
Currently I am planing to only use a single dummy cell and use some kind of foam to support the cells from the opposite side since:
1. It is lighter
2. It is less work :)
3. A foam will prevent the cells from rattling in the box.
Looks good to me.
I had a small crisis today, while screwing the cable into the connector, I torn apart the soldering point with the connector from the Prefboard. lucky I could find some other points and was able to solder it back.
to prevent it from happening in the future while using the light I glued the connectors with hot glue to the board. It should keep everything together :)
After gluing the connector I screwed back the cable and set the board and "dummy" cell in place.
You can also noticed I added a spring,. I did bypass this spring since it is thinner and I am only using a single spring for the negative contact so it will conduct 2.8A in turbo mode
And with the cells and foam, everything fits perfectly (not very impressive since the foam is flexible :) )
I forgot to mention I put some RTV on the cable before pull it through the cable gland to improve weatherproof. I hope it still be possible to pull it out for maintenance.
Today I finished the battery box 
I took some nickel spring/plats I saved from a light or some other battery operated device.
I wanted to use the original contacts plate I took out from the AA battery box (also in the picture) but it was too high for the new cells so I will keep it for another project
I have soldered the two plates together and also added some copper wired behind to improve conductivity.
The 2 raised parts are for the cells and the bump on the left for the dummy cell.
Then glued everything to the lid.
And finally, tested it with charged cells - works as expected :)
I always love the part where it works, fits, etc. :+1:
Sadly, most times it does not....
That’s the modder’s way! Or at least, how it usually goes for me 
After completing the battery box (not really, I still have an Idea for a secrete feature I want to add ), I am back working on the lamp.
As for the battery box, I want to use screws connector for the main power line (to make it possible to replace it without soldering and to enable some field repairs) but I don't have place for full size connector so I had to cut it a bit.
I also removed the protection for the screws. It reduce size but also enable using bigger screwdriver or even a knife to fix the cable.
I also started making a slave board for the 2nd channel (wide beam).
Since I did not find slave board I decided to solder 6 AMCs on top of each other. I choose a little bit less current to keep the wide beam which I use most of the time, closer to the "linear" lm/A consumption in order to save power. Maximum output of about 850 lm is enough for me.
In order to make soldering easier, I cut the middle leg of each IC
And finally glued all ICs together
Next step is soldering ....