This study reports various analyses of the proton activity in brushite CaHPO . 2H(2)O and monetite CaHPO4 considered as potential solid electrolytes in mineral/polymer composites. Volta battery devices are first used to control the migration paths of protonic species through phosphate pellets or brushite/polymer composites. The dehydration process of brushite into monetite is then analyzed from the Volta battery potential difference. Finally, the first results obtained by quasi-elastic neutron scattering analyses are discussed.