A cyclic voltammetric study of the electrochemistry and chemical stability of the poly(vinylferrocene) (PVFc) redox couple, coated on a gold substrate, in aqueous solutions of H2SO4, HClO4 and HCl was carried out. It was found that the anodic peak potential (E-pa) did not depend on the acid concentration in the range (1.0 x 10(-2) to 1.0 x 10(-7) mol L-1). However, the Epa values shifted linearly to less positive potentials when investigated in more concentrated acid solutions in the range 1-5 mol L-1. The slope of the E-pa versus acid concentration graph was found to be in the order H2SO4 > HCl > HClO4. In this regard PVFc behaved very similar to 1,1'-bis(11-mercaptoundecyl)ferrocene (Fc(C11SH)(2)) except for its chemical stability. In H2SO4 media the PVFc was found to be much less stable than 1,1'-Fc(C11SH)(2). The dependence of Era on acid concentration could be used to monitor state of charge of lead-acid batteries. However, for this application Fc(C11SH)(2) would be a better choice because of its superior chemical stability. (C) 2004 Elsevier B.V. All rights reserved.