An air-filled parallel-plate capacitor with capacitance \(C_0\) is connected across a battery that maintains a constant potential difference \(V_0\). While the capacitor remains connected to the battery, a slab of uncharged dielectric material with dielectric constant \(\kappa > 1\) is inserted, completely filling the space between the plates. Which of the following claims correctly describes the change in the electric potential energy stored in the capacitor and provides the valid physical justification?