You might get a cheap charger from amazon that comes with your 18650 flashlight, but that charger is very dangerous as all the 120 volt pins are very close together. The soldering is very shabby. The cheapo charger charges at a constant voltage of 4.2 volts and does not sense the voltage of the battery. Furthermore this only charges at 650 mah.
By replacing the inside with the circuit from a cheap battery bank we get a safer charger as it uses a usb wall plug to bring down the voltage. This charger can sense the battery voltage and will regulate the voltage. The charging current is almost double at 1200 mah.
What you need
- hot glue
- soldering iron
- prying tool
- a cheap battery bank
- a cheap charger
Step 1: Extracting the Circuit
Pry open the battery pack to reveal the lithium battery and circuit.
Leave the wires on if you do not have a soldering gun to make soldering easier.
Carefully pry off the USB port.
Step 2: Dissembling Charger
Remove the screws under the label
Remove the circuit board and de-solder the wires
Step 3: Drilling a Hole
Mark out where the micro USB is.
Then drill a hole that would fit the usb
Step 4: Soldering
Hot glue the Circuit board in.
Solder Black to Black and Red to Red.
Red is positive
Black is negative
Step 5: Finished
Put the Screws back in.
Test that there is voltage
Then you are done