Electricity is added to recharge a battery. A third phosphate group is added to ADP to form ATP.
ATP or Adenosine triphosphate contains adenine, ribose and 3 phosphate groups.
ADP is converted to ATP by the following reaction:
ADP+Pi+energy⇄ATP
The analogy between battery and ATP can be explained as ATP is higher energy form and ADP is lower energy form like charged and uncharged form of the battery. When the terminal or third phosphate is removed from the ATP it becomes ADP and releases energy like a battery. The additional phosphate group when added to ADP forms the ATP molecule like the energy spent by the batteries are recharged by putting in additional energy. Here the additional energy is provided by the third phosphate group.
