This is my first Instructables post, so not sure if I do it right :)
Everytime I needed my batteries charged I was in a rush and had no time to charge them inside the camera. So here is a rushed 1 hour project from leftovers.
WARNING:If you mess with batteries and you do it wrong they can mess with you too, so be careful and preferably let your charger be checked by someone that knows things. :)
Step 1: Get the Correct Charging Board.
To get the correct charging board you need to have the correct charging voltage. I suspected a charging voltage around 4.2 V because of the 3.7 battery voltage. This is usually the case with Li-Ion batteries, but make sure you measure the voltage of the charging pins when the camera is turned on. I don't know if you can turn on a GoPro without battery because I have a cheap (still very good for the price) Chinese Firefly 6s. When you have your voltage you can search for a correct charging board. I got a TP4056 charging board for about $2 per 5pcs on eBay. Here is a link .
Step 2: Make the Thing
I'm sure that you can do a much better job at this but I was lazy and gone jank-style.
To make the pins to access the battery I cut a piece of non-solid copper wire and flattened it out with pliers and then applied some solder. Then to reduce the amount of solder and thereby the thickness of the pins I bend the wires a little bit with my soldering iron and catapulted the solder from it like you do with a brush and water. Note: this can get quite messy. Note: I don't know how to explain this.
I got a piece of cardboard and positioned my battery how I wanted it to be. Then I glued a piece of cardboard next to the battery. Note: Don't put glue on your battery, it won't stick into the camera properly.
Put the "pin wires" inside the battery terminals and position the charging board. Glue it inplace and solder the wires to the B- and the B+ terminals. Don't, ofcourse, swap the minus and plus, you battery can explode.
If you want more than 1 battery charger you can repeat all these steps and connect IN+ and IN- of the two charging boards to eachother. That way it will power all the chargers from one USB cable. I put a switch between one of the two cables so you can turn the other charger off while the other is charging.
If you need any help I'll be there for you!