Red should be positive, black negative - however the battery connector is reverse voltage protected so even if you wire it up wrong it'll be ok.
@Gordon started
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
Red should be positive, black negative - however the battery connector is reverse voltage protected so even if you wire it up wrong it'll be ok.