Free Li-ion cells from old camera battery

It's quite easy to open the external plastic enclosure. I just use my Dremel (you can use an hacksaw) to cut along the the line where the two halves of the plastic casing meets. Pay attention not to go deep as you will cut into the cells causing fire and explosion!

After cutting along the joint, I use a flat screwdriver to pry the case apart. Insert the screwdriver and rotate it to get the enclosure open. In my case there were two Li-ion cells, smaller than traditional AA alkaline batteries, connected to a small circuitboard. Using some pliers, I carefully cut all the metal tabs that connected the cells together and to the circuit. I test the voltage of each cell and surprisingly they weren't dead (3.23V both). Good news!

I charge them up using the TP4056 single cell charger. I solder a wire between the positive of the battery and the B+ of the circuit and another one from the negative of the cell to B- of the charger.