On the first place, not all the energy that the battery is able to supply is obtained. For example, a battery discharged in 72 hours returns approximately twice as much energy as if it were discharged in just 8 hours. Besides, fast discharges produce deformities and the premature disintegration of the plates of the elements, that are deposited at the bottom of the containers in the shape of powder until they short circuit both plates making the battery useless.