Say for a NiCad or NiMH battery, how is battery capacity calculated?
Say I put a resistor across the battery and measured the voltage
periodically. Is it the area of the curve above 1.1 volts, 0.9 volts,
or what?
======
Discharge the fully charged battery at a constant current until the voltage
has dropped to 1.0 volt per cell
A simple constant current drain can be made with a LM317 voltage regulator
used as a constant current regulator up to 1 ampere ,by tying the reference
leg 'downstream' of a resistor connected to the output leg.
Since the LM317 needs some 'head voltage' ,this system works well as from 3
cells in series , hence 3.6 V.
For 12 V and higher battery packs an additional resistor is advisable to
dissipate part of the discharged energy , alternatively you can use a LM
7805 voltage regulator in the same way, without an additional resistor.

Frank GM0CSZ /KN6WH