Some embodiments of the present invention provide a system for charging a series battery, wherein the series battery is comprised of a set of banks which are connected in series, so that the same charging current passes through each bank. During the charging process, the system measures a voltage across each bank in the set of banks. The system then compares the measured voltage with a target voltage for each bank, and adjusts the charging process based on results of the comparisons between the measured voltage and the target voltage.