Recently I bought a usb-charged lithium-powered keychain flashlight. Ostensibly its by Nitecore, but i'm a bit suspicious it might be counterfeit.
OK, it comes, it charges, it works, its bright. Great. Hand it off to Sonya, it can inhabit her keychain w/ the thousands of other things. 1 day later, dead. Sigh.
Small Philips screwdriver, disassemble. Here's what we see:
snoop around with the magnifying glass a bit, its intermittent. It works when the switch is wiggled. Resolder switch, hmm, no change. Then i see it, the LED itself is soldered directly to the board, that is the mechanical strength too. Although its a through-hole LED, it is tacked directly to the PCB, and no other mechanical support (it pokes directly out into the open as you can see). And, that solder joint is not so good. Reflow, we are fixed!