Performance characteristics of a three electrolyte rechargeable acid-alkaline hybrid battery using a PbO2 positive plate and a nickel metal hydride (NiMHx) negative electrode in separate electrolyte of H2SO4 and KOH were studied. This hybrid battery has three electrolytes in a single cell. A neutral K2SO4 salt solution was placed between the acid and alkaline compartments of the cell, in which a cation exchange membrane and an anion exchange membrane, were employed to separate these three electrolytes. The open circuit voltage of this hybrid cell was found to be 2.64V in an electrolyte configuration of 1 M H2SO4 vertical bar 0.2 M K2SO4 vertical bar 2 M KOH electrolyte configuration, compared to 1.92 V in the conventional lead-acid cell in 1 M H2SO4 and 1.40V in a NiMHx cell in 2 M KOH. This hybrid acid-alkaline PbO2/NiMHx battery was shown to operate with a voltage 20% higher than the conventional lead acid battery and 110% higher than nickel-metal hydride battery at 1/3 C discharging rate. The concentrations of the three electrolytes, the dimension of the electrolyte chamber, and other cell/operation parameters with impacts on the hybrid cell performance were investigated. (C) 2011 Elsevier Ltd. All rights reserved.