how to model shortcut in flow battery

Hello,
I am working on a vanadium flow battery model. The model is used by two Tertiary Current Distribution and on Secondary Current Distribution physic fields. You can find a simplified version in app library( v flow battery). I want to do a shortcut (in membrane) on the battery to see what will happened of the battery. I tried to use a external short node but it didn't work. It is a little tricky because the two electrodes are model in two tertiary current distribution fields.
Can anyone give me some ideas how to make it?

Thanks