The requirement is to compute the capacity of the battery in order to calculate the capacity degradation.
The input which can be acquired are current, voltage, relative time, battery level (in terms of percentage).
As per as formula
Capacity = Integral of Current over time. (of discharge cycle)
So the doubt is, does the time here mean from reaching, say, x voltage to y, or from battery level 100% to 0% on discharging?
Basically, how is the interval to calculate capacity is considered?
You have discovered why "battery capacity" is a vague term. Yes, you have to define what the ending conditions are. Usually this is the voltage that the battery should not be discharged below to avoid damage.
If you really want to know what the battery can do for you, it is better to measure the total energy delivered in one discharge. That is the integral of voltage times current. You can still measure capacity (integral of just current) to have something to compare to the official specs.
