It is not possible to directly change the battery parameters during run-time in Simscape models. As this is a physical system might not actually be realistic to do so and we might run into issues. We can off course model battery aging and that would update the parameters in a meaningful way.
One thing that can be done is to use Simscape run-time parameters which allow you to skip recompiling the model when you change parameter values. Alternatively, if you just want to change the load might be an option to use a Controlled Voltage Source or Variable Resistor/Capacitor/Inductor blocks. I hope this helps.
