Hi everyone,
I am using TinyZero board combined with 3.7V Li-Po battery to develop a wearable device that records motion data. Currently, I want to accurately measure the remaining battery level to display the battery percentage or warn when the battery is low, but I am not sure how to read the ADC value from the battery properly.

I tried reading the value from the analog pin A7 (VBAT) and using a simple formula to calculate the battery percentage, but the result fluctuates and is not stable, especially when the device is operating for a long time.

Is there a more accurate way or calibration formula to convert the ADC value to the remaining battery percentage?
Does TinyZero use an internal voltage divider to measure the battery, and if so, what is the ratio?
Is there a reliable library or sample code to monitor the battery level on TinyZero?

I would love to receive support from those with experience. Thank you.