Disclaimer: these torches are bad, they're cheap for several reasons! Unreliable, very short lifespan, bad manufacturing, lacking attention to details. Only advantage in buying them is they're cheap.
That's my humble opinion on what I've personally experienced. People may disagree.
Anyway, one of the ones I own stopped working (in such a similar way as others report, here too) and instead of throwing it away I tried (and succeded) in reapairing it. This may help someone. Here's how.
I'm talking about the A15 model, as mentioned in the starting post. I suppose other models are very similar if not identical.
The culprit seems to be the internal pcb which is not fixed in place, it rotates when you close the battery case and tears the wiring inside.
The details follow.
First sign of failure was the coloured leds not working. After a short time (I'm talking minutes) the white leds stopped working also.
The torch didn't flood nor did the buttons show any sign of damage.
I opened the battery case, removed the round metal spring holding the pcb in place and immediately saw the wiring connecting the main pcb to the external ones (those inside the front case, where buttons and leds are mounted) being torn apart (not all, just a few ... well, several!).
It seems like the rounded metal spring holds that pcb in place but doesn't stop it from turning when you close the battery case, like ... you screw the case (with the batteries inside) and because of friction the batteries' + pins force the pcb to rotate with it a bit. You repeat the process several times and the pcb rotates so much that it breaks the wiring hidden behind it.
View attachment 676803
2x4 small black wires connect the main rounded pcb to the front casing where leds and buttons are mounted (from point B to point C).
Those are so tiny that cannot hold the stress and become loose after a while (see floating wires on A).
Other 4 biggish wires (red and black) survived the stress. I guess they provide current to the LEDs.
I simply soldered back the tiny wires and everything works again. No LEDS has been harmed in the process
You need steady hands, but if you're used at soldering it's not that difficult, it's not like SMD or similar.
In order to prevent the same from happening again I placed a small plastic thingy inside the oval notch on the PCB (point X), where it aligns with underlaying rounded notch on the casing (point Y), hoping it will stop the PCB from rotating again under the mechanical action of the batteries. It's not a fool proof solution, I will try and block the PCB in a more definitive way in the future, but at the moment it works.