Preventing Jump in Battery voltage/percentage while board is plugged in.

[NicholasCessna]

I am working with the Wifi32 V3. I am using the heltec_vbat() and heltec_battery_percent() functions from the library. I have the percentage displayed on the OLED. I implemented a low pass filter to keep from rapid battery voltage fluctuations and in turn fluctuation in the percentage read-out. My issue, when the board is plugged in to charge, there is a battery increase by 10%, give or take, due to the increase in voltage from charging. When unplugged there is an equal drop reflected in the voltage/percentage. I was considering implementing a bool flag isCharging() and using one of several available ways to detect if the board has been plugged in. My main issue is how can I determine an accurate difference between the charging voltage of the battery and the battery`s actual voltage (other than using the observed difference of 10%)? Do you have any good suggestions?