An electrochemical battery cell comprising an anode having a primary anode active material, a cathode, and an ion-conducting electrolyte, wherein the cell has an initial output voltage, Vi, measured at 10% depth of discharge (DoD), selected from a range from 0.3 volts to 0.8 volts, and a final output voltage Vf measured at a DoD no greater than 90%, wherein a voltage variation, (Vi−Vf)/Vi, is no greater than ±10% and the specific capacity between Vi and Vf is no less than 100 mAh/g or 200 mAh/cm3 based on the cathode active material weight or volume, and wherein the primary anode active material is selected from lithium (Li), sodium (Na), potassium (K), magnesium (Mg), aluminum (Al), zinc (Zn), titanium (Ti), manganese (Mn), iron (Fe), vanadium (V), cobalt (Co), nickel (Ni), a mixture thereof, an alloy thereof, or a combination thereof.