In this study, co-doped and undoped MnO2 samples were prepared by redox reaction in acidic medium. X-ray diffraction patterns of pure and doped samples revealed that they crystallized in the alpha-form with a (2 x 2) tunnel structure. Chemical analysis indicated an increase in the concentration of K+ cations upon Co doping resulting in higher thermal stability. Magnetic properties show the coexistence of Mn4+ and Mn3+ valence states, with reduced amount of Mn3+ ions after the doping process. Co-doped MnO2 has better rechargeability and capacity retention than pure alpha-MnO2, but the reduction of the capacity fading occurs at the expense of the initial capacity.