A method and apparatus of the present invention are designed to equalize cell-to-cell imbalances in a multi-cell lithium battery system. A time-to-balance parameter is calculated for each cell at the beginning of charge, and balancing occurs for each cell having a positive time-to-balance at the beginning of charge. Alternatively, the time-to-balance parameter is calculated during operation of the battery system and equalization of the cells occur in-sit based on the time-to-balance values.