DIY 18650 battery hack conversion

The great reason for adapting 18650 batteries to work with your everyday gadgets is this:
In my humble opinion, I think 18650 batteries are an awesome upgrade to the humble old timey AA. They charge much faster, hold more energy, and in recent years had become super affordable at something like a dollar a piece. If you are reading this on an average laptop then there are probably three of them inside it -- try doing that with AAs!
IMPORTANT: 2xAA ~= 1x18650

To get started you will need:

This is going to be a growing list of gadgets to which I applied the 18650. The results are not pretty but this is not called fashion either:

  • Photography flash trigger (originally 2x AA, replaced by 1x 18650) and receiver (originally mini 12V, replaced by 1x 18650)
  • Speedlight portable flash (originally 4x AA, replace by 2x  18650)
  • Hair trimmer charger (originally a proprietary wall-wart with quite a long cable, universal AC to 3.7V, replaced by 1x 18650)
  • medium power bike helmet light, made from 1x front froglight + 1x tail helmet light -- RIP
  • Bluetooth speaker that worked on 4xAA, now works on 2x18650, the batt door does not close but that's a todo for another time. -- RIP
  • Ikea cordless screwdriver, even though it had a 18650 built in, it got converted to a external plugin config. This way when it runs out of charge, a fresh battery can be plugged in and work can continue.