Obviously the simplest method is too place a resistor across the positive and negative ends of the battery and then measure it with a meter.
This method has a few drawbacks....your resister MUST be large enough (wattage wise) to disappate the heat you will be generating at the current rate you are using. Another drawback is that as the battery discharges, the voltage tends to decrease which means the current rate changes too....so while you may choose a resister that gives you a 100mA rate at the beginning, it will change as the battery depleats itself.
Most modern chargers/analyzers have some type of differential/comparator circuits that look at the voltage and changes the resististance applied to maintain a constant charge/discharge rate.
I would like to see someone come out with a simple battery tester that lets you select various load rates instead the the cheapie testers nowadays that say they put a load on the battery and it is usually in the neighborhood of 10-100mA.
