ESP8266 Power Supply: Running wifi sensors from a LiPo cell

As I showed with the Long Term data logger test you can run an ESP8266 for almost three months and post temperature and humidity every 10minutes to the internet from 3AA batteries. But 3AA batteries are quite spacious and fitting them and the ESP8266 into a neat little box will get you a very bulky product.
But which modern mobile devices use AA batteries anyway? LiPo batteries seem to be the obvious choice for commercial products, so why not use them in your DIY projects? Well, there are a few problems that you have to master in order to do so:

  1. LiPo batteries usually have a nominal voltage of 3.7V but an actual cell can have a voltage from around 3.2V (empty) up to 4.2V (fully charged). And 4.2V is far too much for the VCC of a ESP8266.
  2. LiPo’s don’t like over- or undercharging very much. They can overheat and catch fire and who likes to have a fire hazard in the home?
  3. LiPo cells come in various forms and are equipped with different features. Which one is the right for your project?
I thought that there must be an easy to use module that would solve all (or at least the first two) problems mentioned before. And it turns out there is!
It has a few cool features but is also a bit pricy: the SparkFun Lipo Charger/ Booster. The reason why it caught my eye: by changing a solder bridge you can adjust its output from 5V to 3.3V which is a perfect fit for the ESP8266!
With the built in JST connector you can attach standard LiPo cells very easily and charge them through a micro usb port while an LED will tell you about the charging state. 

Experiment

To test the efficiency of the module I am running a little test: the module powered by a 500mAh LiPo cell feeds a NodeMCU V1.0. The ESP8266 connects every 30 minutes to thingspeak and posts measured Vcc Voltage, cycles at the moment of the post and number of retries to connect to Wifi. After that it returns to deep sleep and only wakes up 30 minutes later

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Shopping

The original module costs at Sparkfun $19.95 and is relatively expensive compared to a $7 NodeMCU V1.0. Of course you can also find cheap ripoffs for $9.90 at Aliexpress
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