Laser holographic interferometry was utilized to monitor the volume change in lithium/iodine poly(2‐vinylpyridine) (P2VP) batteries for the entire discharge at high discharge rates. Two cathode chemistries were used, one containing P2VP with a molecular weight average of 22,000 and the other containing P2VP with a molecular weight average of 54,000. One of each cell type was discharged across constant 1 kΩ (approximately 300 μA/cm2) and 5 Ω (approximately 120 μA/cm2) loads. In all cases, the cells initially expanded nonuniformly. This was followed by more uniform expansion and then a transition to uniform contraction which continued until end‐of‐life. The batteries manufactured with the cathodes containing P2VP with a molecular weight of 22,000 exhibited net contraction relative to initial dimensions and experienced a smaller initial expansion and an earlier transition to contraction, as compared to the cells manufactured with cathodes containing P2VP with a molecular weight of 54,000, which exhibited a net expansion with respect to initial dimensions. The differences observed between the two cell types are explained by a dependence of the mechanical properties of the cathode on the molecular weight of the P2VP. Both cathode types become more pliable with discharge, enabling a mechanical restructuring of material within the cathode to occur. This results in battery contraction. No distinct electro‐chemical events were noted concurrent with the expansion, transition, or contraction stages. Normal high rate behavior and end‐of‐life behavior were observed in all cases.