Pixl.js with Wifi (ESP8266 ESP01s) - SOLVED

I did measure the 3.3 and ground (using a regular multimeter) and I see it turn on. stay on and when the lights go out it goes down to 0v so it's being killed

That's perfect. Sounds like a hardware issue then, and I'd hope a big capacitor would go a long way towards fixing that. It's strange that it doesn't cause the Pixl itself to reboot?

What happens if you measure the battery voltage when it happens? It's possible that there's an issue with the battery itself rather than the voltage regulator.

You could try turning the RGB LEDs off (or dimming them) if they were on?

I forget what's on the Pixl badge now. It was supposed to have an MCP1703T like is on the Pico (250mA average, 400mA peak) but I accidentally ordered the wrong package and we had to use another part in a hurry. As it happens that actually had a pretty good spec, it just had a higher quiescent current (but that's not a big deal for the badge).