Power of battery, when charged is given by P1 = V1I1 Electrical energy dissipated id given by E1 = P1t1 E1 = V1I1t1 = 15 × 10 × 8 = 1200 Wh Similarly, the electrical energy dissipated during the discharge of battery is given by E2 = V2I2t2 = 14 x 5 x 15 = 1050 Wh Hence, watt-hour efficiency of the battery ⇒ η =