Mechanical degradation in fibrous composite electrodes in use in NiMH (nickel metal hydride) batteries is being studied. NiMH cells exhibit failure in the positive plate due to swelling induced during the electrochemical reaction, which leads to gradual breakdown of the connectivity of the substrate microstructure. Particularly, loss of electrical conductivity as related to losses in mechanical properties upon cell cycling (constant current cycles with substantial overcharge) are being investigated experimentally. These properties are measured for the dry substrate material before and after battery cycling, and the losses observed suggest key failure mechanisms include mechanical damage. Results suggest tradeoffs between use of higher density nickel substrates and improved energy densities using mechanical and resistivity proof tests.