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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.
@tage
the 3.3V regulator is very tiny, and I would not connect a 12V battery and expect it to work. a look at the datasheet for the MIC5205 shows that the temperature rise is about 220 degrees per Watt. if the Espruino draws 35mA and we connect a battery with 15V then the dissipation is 0.41W which means that we may reach over temperature and the regulator shuts down. it is better to use a 5V USB charger of the type you plug into the cigarette lighter in your car, between your battery and the Espruino. this way you can add some additional load to the 3.3V (about 100mA I believe). or you can power your extra gadgets from 5V.
be aware of the danger when you connect a battery. the battery voltage can be above 15V and there is an inrush current at plug in because the capacitor at the input of the 3.3V regulator is quickly charged. there can be an overshoot in capacitor voltage because of the inductance in the battery leads (an LC resonant circuit is formed) and if the resistances are low, the capacitor voltage can theoretically double when you plug in the battery. this would kill the regulator.
if you are working with solar panel charging of the battery you should also be aware that the voltage from the panel will be as high as 24V when the battery is not present.