Cannot save and run code stops when connected to a battery

Hi!

Which board are you using? Do you save just by typing save() after an upload, or by some other means?

What you're doing looks fine. Have you tried adding blinking some of the on-board LEDs on and off to see if Espruino itself thinks it is doing something? It might be an electrical issue rather than a software one.

Also, a while back we changed to using neopixel.write for sending data to neopixels. What you're doing should still be fine, but if you use neopixel.write then it's a bit more readable, as well as more portable to different platforms (like Puck.js if you ever wanted to use that).