A new electrochemical cell was designed and constructed to enable in situ measurements of the performance and internal resistances of lead-acid test electrodes in a vertical position during cycling at well-defined degrees of compression. The AGM separators used were combined with microporous paper separators to prevent short-circuiting by conducting bridges of lead dioxide. The test cells were subjected to pressures in the range 0-8 N/cm(2); the compression decreased the positive active mass resistance and increased its cycle life.