Hello Matthew,
to make that value editable, you will need to create a custom block and modify the battery. To do this, you would use the powergui block customize function. Customize the battery block, then delete the gain block and replace it with a product block. Then you can add an input port to be the thermal resistance so that you can control it externally while the simulation is running. Most specialized power systems blocks cannot have their parameters changed durring simulaiton unless modified like this.
Regards,
Joel
