Charging methods and systems are provided which charge multiple cells directly from an AC source, by adjusting, momentarily, the number of charged cells to the momentary voltage level provided by the AC source. Cells are rapidly switched in and out to correspond to the provided voltage level, and the charging level of each cell is regulated by the switching order of the cells—determined according to cell characteristics such as state of charge and state of health. Advantageously, charging losses are reduced significantly in the disclosed systems and methods, and an additional level of cell control is provided. The charged assembly of cells may be arranged and re-arranged in various configurations to optimize the charging scheme, e.g., to equalize the charging states of the cells to simplify the use and improve the efficiency of the cell stack.