The battery system of this invention continuously regenerates the electrodes of the battery in-situ and on-time as the electrodes are consumed during discharge, which concurrently generate electric current. The continuous in-situ and on-time regeneration of the anode is achieved by a supply of reducing materials in the battery compartment that is in contact with the anode. With the use of high energy density reducing materials, the energy density of the battery system is increased significantly. When the reducing materials are consumed, the reducing materials can be replaced with a supplying device. With the use of specially designed supplying devices for reducing materials, recharging battery system is more convenient, safe, fast, and can be operated repeatedly.