I finished the EasyEDA version of the board a while ago, and I have sent the design files to JLCPCB for assembly. They arrived today, and I was quite surprised to see that they just work, without any problems or mistakes:

Even the original laser-cut case fits, though the QWIIC socket is a bit of a tight fit in there.

Encouraged by this, I proceeded to testing the battery power, and lo and behold, it works as well!

Then came time for checking the sound. I completely changed this, got rid of the transistor driving the speaker, and instead used an I2S amplifier. And it works very well, and is pretty loud even at the lowest gain setting.

There is however a slight problem with this when running on battery power. You see, the speaker is so loud, that it makes the battery voltage drop, which causes the backlight to dim and sometimes even the display – the only part that really needs 3V for power – will sometimes reset and show the white screen of death. That only happens with the loudest sound I have in my games – the explosion – but it is a problem.

So what can I do with it? I will try and see if I can squeeze a boost converter circuit in there, to keep the battery voltage stable even when the poor little things are overloaded. It should also prolong the battery life, so yay. The problem is that I have never done this before, so I'm a bit worried how it will go. The datasheets seem to be simple enough, though.