Why is the Energy in Capacitance Formula (CV^2)/2 Instead of QV?

[semc]

Hi, why is it that when u integrate V wrt to Q u get (CV^2)/2 instead of QV since voltage across is constant?

 

[Doc Al]

The voltage across the capacitor is not constant. The voltage delivered by the battery is constant, so the total energy from the battery is QV, but not all of that energy ends up in the capacitor.