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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.
@Gordon
Yeah, so with blue LEDs you don't have much voltage in hand. Even with the 3v from the coin cell it's going to be a bit tight (but the good news is it'd so 'on edge' that moving to a schottky will help you out noticeably).
Personally, what I'd suggest is to use a small LiPo rechargeable battery and a LiPo charger board (which will have a USB connector on it anyway). You can then power the watch direct from the LiPo, and when you plug into USB it'll charge the LiPo which will have the effect of also powering the watch.
With a bit of searching local shops or eBay/Amazon you may even find a cheap mini torch/power bank that has a LiPo battery, charger and USB connector in it that you could use for parts.