When the final long term test of power consumption of my Wemos d1 mini temperature monitoring system was complete:

 

Power Consumption of a Wemos D1 mini ESP8266 - Long Term Test 3

 

I decided to try recharging the battery - from a mobile phone charger - whilst the Wemos d1 mini was still connected, so that I could monitor the charging process.

 

Battery Charging 1

After charging the battery for just over 2 hours I had to go out, leaving the house empty, except for #sadiethecat1409 (Instagram). I disconnected the charger because I felt uneasy about leaving it charging unattended.

 

While I was out I had the idea of charging the battery from the mobile phone power bank that failed to run the Wemos d1 mini in my first blog in this series, here is the result:

 

Battery Charging 2

 

After about 2.5 hours on the power bank, the battery voltage, as measured by the A/D on the Wemos d1 mini, has reached 4.31V. By this time, I would have hoped that the blue LED on the battery shield would have come on to indicate that the battery was fully charged. Alas it didn't!

 

The series of blips which follow the plateau are:

  1. Disconnecting the power bank and reconnecting the mobile phone charger, to see if the charger delivered a higher voltage - it didn't
  2. Re-connecting the power bank
  3. Disconnecting the power bank and leaving the Wemos d1 mini to run for a while.

 

Conclusion

 

Using a mobile phone power bank provides an ideal method of recharging the battery of a system designed to run in an environment where there is no mains power.

 

I think this is a better approach than one in which the battery is replaced, because replacing the battery could cause disturbance to the system and will result in a (hopefully brief) interruption to the system function - this may or may not matter.