Extending wiring on 7 led flashlight

I've searched through the forum and can not find an answer to what i'm certain for most of you is a very easy. I admit my complete ignorance and appreciate any help.

my problem-- So i have a 7 led flashlight that runs on 3 -3.7 volt 26650 batteries. I attempted to remove the head of the flashlight and wire it through a pvc tube to place the battery tube (powersource) further away. About 3.5 ft away from the flashlight head. I used thick 12 guage wire and it appears i fried the circuit board. Any ideas on what i did wrong and how to correctly determine the proper wire size needed?



product specs:


Description

Features:


* This torch uses of a 7x CREE XM-L2 LED, producing very bright beam of light.
* Output bright can come to above 12000 lumens(lm)
* Internal wiring applies the high efficient booster circuit,and can utilize the batteries in the largest extent
* The body of this flashlight is built of aircraft-grade aluminum alloy, and it has a very solid construction.
* Hard-Anodized finish; Anti-abrasive, free-scratch, shock-proof.
* Ultra-deep trench structuresi Skid-proof effect is excellent when diving
* This flashlight uses a textured reflector(rather than smooth reflector).The beam from a textured reflector is more even, with a more gradual transition between the hot spot (the center of the beam) and the spill (the periphery of the beam).

Specification:

* Emitter Type: CREE XM-L2 LED
* Light Color: White
* LED Quantity: 7
* Waterproof: Under water 50 to 100 meters
* Battery Configurations: 2pcs 18650/2pcs 26650/3pcs 18650/3pcs 26650 Battery (Not Included!)
* Voltage Input: 8.4v
* Switch Type: Twist
* Modes number:Low > High > Stroe
* Mode : To adjust the brightness gradually
* Brightness: 12000 lumens maximum brightness
* LED Lifespan: 100,000 hours
* Material :Aluminum
* Lens: Coated Glass Lens
* Reflector: Aluminum textured reflector
* Casing Color: Army Green
* Size(mm):223/(290 if plus the extend tube)L * 63(TD)*40(WD)
* Weight: 500g

Packaging Contants:

* 1x 12000Lm Scuba Diving 7x CREE XM-L2 LED Torch (Battery Not Included)
* 3x Battery Convertion Tube(When use the 18650 Battery)
* 1x Extend Tube

First of all, the problem is NOT the wire size. Anything 18 AWG or larger should be fine. You would see almost no difference between wire sizes until you get smaller than 18 AWG.

There are only two things I can think of that might have been wrong. One is that the battery could have been connected backward. In some cases this just means the light won't work. In other cases, the light is damaged. Unfortunately, the latter is much more common in inexpensive lights.

The other thing that might have gone wrong is that the light head didn't have proper heatsinking. In all liklihood, the battery tube is an important part of the heatsink, especially if the light is operated in air. When you removed the battery tube and replaced it with plastic, it significantly degraded the heatsink. Even worse, some diving lights are not designed to be operated in air. Heatsinks work many times better in water than in air, so a light that runs fairly cool in water can overheat in air.

If the problem was reversed battery, the light would not have lit at all, and would have failed almost immediately. If heatsinking was the problem, the light would have worked fine for some period of time, from a few seconds to a few minutes or perhaps even more, before failing.