How do I connect a four way key in a potentiometer?
If those two cells are truly isolated, then a simpler circuit is possible. You don't need both changeover switches to select between their EMF's, only one is necessary, and that can be implemented with your 4-way key.







simulate this circuit &ndash; Schematic created using CircuitLab

Close SW1 to select V3, or SW2 to select V4

If you do want to switch the positive terminals as well, then you need a six-way key, or two of the four-way ones.