I use an ESP8266-12-E microcontroller as basis for an outdoor sensor measuring and sending temperature over wifi to a server. I soldered a DS18B20 temperature sensor (+resistor) onto the chip. The power is provided by 2AA 1.5V batteries (=3V). When outside temperature is above -4°C/25°F, everything works fine. However, when temperature drops below, the ESP8266 doesn't wake up from deep sleep anymore. The ESP is supposed to work with 3.3V.
My first idea why this fails at low temperatures is that the batteries (alkaline) won't work at those temperature. So I replaced them with Lithium batteries. However, that won't work either.
Now I think the problem is that -although using Lithium batteries- low temperatures causes the batteries to not supply enough voltage for the microcontroller. Do you think there could be another reason (like faulty soldering points) why that won't work?