Consider schematic below. 

![schematic](https://i.stack.imgur.com/WWMlK.png)

[simulate this circuit](/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fWWMlK.png) – Schematic created using [CircuitLab](https://www.circuitlab.com/)

With a DC source we can use this arrangement to find the force between the plates of the capacitor. We can do this by finding the mechanical work done pulling the plates apart, the change in the energy stored in the battery and the change in energy stored on the capacitor. I have been told (by more then one professor) that the energy stored in the battery is of the form \$QV\$, where \$Q\$ is the charge on the capacitor (the sign may be negative). But I think this is wrong, this formula says that when \$Q\$ is \$0\$ (i.e. when the capacitor is first connected) the energy stored in the battery is \$0\$. This to me is nonsense. I think the energy on the battery would be better expressed as \$E\_0-QV\$ where \$E\_0\$. Is my formula better? And in the general case what is the energy stored in the battery?