Answer
The energy stored in the battery during charging is less than the energy that can be extracted from it. There is loss in the wiring and in the internal resistance.
Work Step by Step
During the charging process, some of the energy supplied goes into heating up the wiring, and heating up the battery due to its nonzero internal resistance. The joule heating process is characterized by a power of $I^2R$.
This thermal energy leaks into the surroundings and is not stored in the form of chemical energy.
The energy stored in the battery during charging is less than the energy that can be extracted from it.
