Difference between analog signal and battery voltage
The idea is fine, but 220k seems rather high. You should check the specs of the ADC module, there should be an indication of the maximum input impedance (typically around 50k for ADC integrated to most MCUs). Use resistors with values lower than this.

Hint: you could also use a potentiometer instead of the lower resistors (closer to ground), so you can easily adjust the value. Keep at least one upper resistor and make sure you choose values that guarantee that the ADC input voltage rating is never exceeded.