DIY Lithium Battery: 8.4V/4.2V Dual Output Pack

If you are interested in DIY lithium battery packs, you may want to check out this article.

If you happen to have an old 9V battery, you need to remove the internal core and keep only the outer casing.

If you happen to have two 500mAh lithium batteries.

If you happen to have a USB charging module that charges up to 4.2V.

First, find a double-pole toggle switch, draw the circuit diagram, and then you can start building.

Solder everything according to the diagram and apply glue to secure it.

On the base board, when you toggle the switch to the left it outputs 8.4V, and when you toggle it to the right it outputs 4.2V for charging.

Solder wires to the terminals.

Prepare to assemble the casing and add insulating tape between the circuit board and the battery.

This is what the finished assembly looks like. Although it is not very aesthetically pleasing, it works very well.

Switch to the 4.2V position to charge it fully.

Switch to the 8.4V position for output.

Finished. It is still very simple.