I would say this method is impractical for testing e-bike batteries, because of the high current drain in this application. Say the maximum current draw is 10 amps (but I suspect much more*). To use this method, the battery is loaded to the maximum level for a short period of time, and the response measured. For a 48 volt battery, you would need a load resistor that will dissipate 480 watts.
If you want to pursue this idea, please start your own thread on the topic.
* One battery I looked at has a C(charge rate) of 7 amps. Discharge rates of 5C or higher look common, which would be 35+amps, and 1680+watts.