What does the charge counter in battery indicates?
I checked the Android source and the value shows your remaining battery capacity in microampere-hours.

BATTERY_PROPERTY_CHARGE_COUNTER
Added in API level 21

public static final int BATTERY_PROPERTY_CHARGE_COUNTER

Battery capacity in microampere-hours, as an integer.

Constant Value: 1 (0x00000001) 


Source - Developer.Android.com