I am working on SOC estimation of battery for EV's, I want to extract the real battery data through the experiments on battery, so i want to know what exactly the equipment's i need to perform the experiment ,I searched about it and found programmable DC source , programmable electronic load, DAQ etc. But my question is why programmable is it possible to do with fixed dc power source? I want to know what exactly the need of programmable power/load, what characteristics we need in them? and how all this connected in closed loop for extracting the data.