Kiwi monitor is an open source CO2/Humidity/Temperature sensor intended for monitoring the quality of the air in a room. Kiwi was created to support teachers with a notification to ventilate their classroom.
Need to read a bit more, but this video shows a simple resistor to the analog pin, to later read the voltage levels. If they start dropping: you know the battery is decreasing...
Need to read a bit more, but this video shows a simple resistor to the analog pin, to later read the voltage levels. If they start dropping: you know the battery is decreasing...
https://www.youtube.com/watch?v=rfPwOtoGO4E