Energy stored in a battery, formula?
Total Energy stored in the capacitor, =   QV/2 = 0.5 CV^2

where,

Q = amount of charge stored when the whole battery voltage appears across the         capacitor.

V= voltage on the capacitor proportional to the charge.

Then, energy stored in the battery = QV

Half of that energy is dissipated in heat in the resistance of the charging pathway, and only QV/2 is finally stored on the capacitor.

We cannot say that Q=0 because as soon as you connect the battery in series with the parallel plate capacitor, it starts charging the capacitor. But if you say that Q=0 , this implies that there is no battery.

Initial charge, Q = 0 means that time before you connect the battery, say at t=0, the charge on the capacitor is zero.