I recently stumpled upon this nice 3D printed 18650 sized battery case for FPV goggles. As i needed some more batteries for my Skyzone SKY-02 FPV goggles i gave it a try.
I opened a “broken” and no longer charging Lenovo Battery pack and removed the 6 Li-Ion Cells. They turned out to be 18650 sized cells and a quick google search told me they were Sanyo UR18650FM cells with 2600mAh. Modern Laptop battery packs are monitored by a special charge managing chip. If this chip “thinks” the pack went bad it will refuse to charge. So often those packs have at least some fully intact cells. I was lucky, mine contained 6 fully working cells.
So with 6 working cells i started assembling the Packs. First you need to print the case and a lid. It is a bit tricky to get it sliced/printed right due to the thin walls. Experiment a bit with the settings of your printer until you get nice results.
Next, take the batteries apart and mark the ones used in pairs. We will use those pairs to make our battery packs. Cut the flat metals that connect the cells to each other but make sure to keep as much of the metal as possible on the cell. Make sure to test the Cells individually using the Li-Ion setting of your RC Charger. It is important to use the Li-Ion instead of Li-Po mode as the discharge characteristics and the discharge cut-off voltage differs.
Connect the cells according to the diagram. Take the biggest soldering tip that you have and make sure to solder not longer than some seconds. Ideally you kept the metal taps long enough that you can solder on those. Direct soldering on the cell should be kept to an absolute minimum, this can get quite dangerous if you solder for to long! If you are not familiar with soldering battery packs or you are unsure ask someone for help! After Assembly charge the cells individually using the balancer plug. Next: go out and fly 😉