Proton-conducting composites of heteropolyacid hydrates (phospbotungstic acid, PTA and phosphomolybdic acid, PMA) with dispersoids such as insulating Al2O3, Al2(SO4)3·16H2O and (NH4)10W12O41·2H2O are prepared for use as possible solid-state electrolytes in batteries. Bulk electrical conductivity as a function of composition is reported. Rechargeable solid-state proton batteries are fabricated and characterized. A cell with the configuration Zn+ZnSO4·7H2O+MH x |PMA+APT|PbO2+V2O5+C+E gives an open circuit voltage of 1.5V and can run for >850h at a current drain of 2.4μAcm−2. The cell can be recharged without much loss up to 18–20cycles.