I developped several systems based on ESP8266, but this chip has a low power consuption called "Deep Sleep".

I decided to run a simple test application which would measure Temperature and humidity every hour and to uplad the data to an Azure database. How long would it last ?

The test was quite disapointing as it ran for about a week on a 500 Mah battery. A quick analysis showed that most of the energy was not drained by the ESP8266 chip itself but by the battery adapter shield!!

I modified my circuit to add a low power timer cutting the current before the shield...  and the device could then run for three month.