In the steady state, the energy stored in the capacitor is :

When the capacitor plate acquire full cahrge 0 q , there will be no current in the capacitor arm. Applying Kirchhoff’s second law to the current carrying circuitiR1+R2=E1−ir1 or  i=E1r1+R1+R2Now Va−Vb=−iR1=−E1R1r1+R1+R2and VC=q0C=E2+iR1=E2+E1R1r1+R1+R2Now energy stored in the capacitorU=12CVc2;=12CE2+E1R1r1+R1+R22