D batteries to 20700 adapter

Create an adapter for a 20700 battery to replace 2x D cells in series with protection and charging ability.

BOM:

• 20700 battery (or 18650 with an adapter)
• Lithium-ion battery charing and protection board
• Some spare small wires
• About 10cm of solid copper wires to use as positive and negative terminal
• A diode to drop your voltage down around 0.4-0.5v. Only needed if your appliance doesn't tolerate the 4.2v of lithium cell at max charge. My gas stove didn't so I added it.

TODO: move the charging board to positive side so the charging USB port won't stick out at the middle and can be used for appliances where there are no tolerance for it at all. Probably won't do it though as I'm done with this project and it's working fine for me.

Included Fusion360 file in case anyone want to make remixes.