Windows Mixed Reality Controller Self-Rechargeable Battery Mod

This mod is for all standard WMR controllers.

Unfortunately, the Samsung Odyssey controllers are currently not supported! If someone makes a copy of the Odyssey controller battery cover, I'd be happy to modify it to work; or alternatively someone can use my blueprint here to make a fully compatible cover from scratch. I'd love to be able to use this on my Odyssey too! :)

Disclaimer
This mod involves using a lithium ion 14500 battery that the Windows Mixed Reality controllers were not necessarily designed to work with. Although evidence currently suggests the mod is safe, that is not an absolute certainty and there is still an element of risk involved.

By default WMR controllers use two AA batteries operating in series for a combined total of 3v. This modification uses a single USB rechargeable Li-ion 14500 battery operating at significantly higher voltage: 3.7v (4.2v when fully charged). The battery is also recharged while remaining inside the controller; some of the chargin