

Apple sources the worse lithium batteries known to man, they last a year and destroy themselves. I have no idea why you’re bringing Apple to this discussion.
I’ve dealt with Chinese devices with batteries that still worked fine six years after being bought.
The Wii board is fantastic for trimming. It sips power and can be trimmed to a specific shape that is tiny and still work. Pretty much any Wii portable or GameCube mod you see nowadays is a Wii board trimmed up, which is fantastic, because the Wii sold over a hundred million units whilst the GameCube did not.
If you want a “homebrewed Wii system made with modern components” you’re describing Dolphin running on any compute board. Those exist too.