ESP8266 Community Forum

Can anybody recommend me a common type battery that I could use to power an ESP 03?

I see the ESP uses 3.3V, and the AA batteries are 1.5V each, and if they will be weared off, it will drop below that. So I'm not sure x2 is a good solution.
Do you think it's safe to use AA batteries x3?

Has anybody here tried powering the ESP using batteries? Did it last a decent amount of time like this (several weeks)?

There are plenty of people reporting that they have run their modules down to ~2.2V. There seems to be differences in operating voltage and firmware used but there isn't any clear evidence of this yet. If you want to run off of a bttery a Li-ion would be a better choice if you don't plan to use any power control (regulators). A Li-ion will briefly start at ~4.2V (which isn't good since the max voltage rating of the ESP8266 is 3.6V) but it quickly goes down to ~3.7V and stays there for almost all of it's operating life. The problem with working with Li-ion is that they don't like to be fully discharged, they cost more than alkaline, and you have to charge them.

Alkalines are nice and cheap but as you mentioned their voltage changes with power level and they span a large range. Maybe the simplest most reliable circuit would be to use 2 AA followed by a booster than is able to boost from 1.8V. This should, in theory be the best bang for your buck (sorry for the English slang).

If you put the ESP8266 in deep sleep you'll be able to operate for over 1 year but then your module wouldn't be doing anything either! Power consumption all depends on what you doing in your code. You can get away with about 70mA when operating the WiFi so as long as you keep your connections brief you can last quite a long time.