Abstract: A method of and apparatus for centrally monitoring the capacity of batteries in a battery string includes electrical leads connected to each battery terminal of the battery string. A capacity testing system a) switches between the electrical leads for sequentially selecting the leads associated with the terminals of each battery, b) measures the internal resistance of the battery associated with each selected pair of electrical leads, c) compares the internal resistance of each battery cell to an internal resistance threshold, and d) triggers an alarm when the internal resistance of a battery exceeds the internal resistance threshold.