I have a 3.7V battery and I want to measure via A0 pin on ESP8266 (Wemos D1 mini) voltage. As far as I know, there is already a series resistor on A0, specifically I mean 220K and 100K. Can I connect this battery directly to A0 for measurement? Or at least a 10K resistor must be used. This is the maximum I have at home, so I ask.
The 100k:220k voltage divider on the WeMos is designed for ~3.3volt.
Just connect a 100k resistor between +battery and A0 of the Wemos.
That 100k:320K divider is now able to measure to ~4.3volt.
Leo..