Please show work for a good rating. A rechargeable battery has an emf of 13.2 V

Question

Please show work for a good rating.

A rechargeable battery has an emf of 13.2 V and an internal resistance of 0.940 Ohm. It is charged by a 14.7-V power supply for a time interval of 1.90 h. After charging, the battery returns to its original state as it delivers a constant current to a load resistor over 6.38 h. Find the efficiency of the battery as an energy storage device. (The efficiency here is defined as the energy delivered to the load during discharge divided by the energy delivered by the 14.7-V power supply during the charging process.) Your response differs significantly from the correct answer. Rework your solution from the beginning and check each step carefully.

Explanation / Answer

current in battery while charging = ( 14.7 - 13.2 ) / 0.94 = 1.59574468 A ..

so energy delivered by 14.7 V = current * emf * time = 1.59574468 * 14.7 * 1.9 = 44.5691489124 Watt-hr

energy stored by battery = current * emf * time = 1.59574468 * 13.2 * 1.9 = 40.0212765744

so efficieny =( 100* 40.0212765744 ) / 44.5691489124 = 89.79592 %

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