With the development of the society, more and more electrical apparatuses use rechargeable batteries as power supply for the convenience of users. According to different desired power, the power supply voltages of most electrical apparatuses are in a range of 6V-120V. For example, the power supply voltage of an electrical bicycle is about 36V, which is supplied by a battery array consisting of 6 series-connected cells with a cell voltage of 6V or 3 series-connected cells with a cell voltage of 12V. When the cell voltages of the cells are low, the cells should be charged. If each cell is charged separately, a large mount of charging apparatuses and/or charging time are needed. Therefore, a battery charger with a charging voltage of 36V is usually used to charge the whole battery array at the same time. Presently, most of battery chargers available in the market only have two input/output leads, which are connected to the positive and negative terminals of the battery array. Such battery chargers could only control the total voltage of the battery array, thus, the cell voltages of individual cells would be unequal due to the discreteness of the cells occurred during the manufacture of the cells and unequalization of the cells occurred after several times of use. When the cell voltage of a certain cell is too high, the cell would be over-charged, and the electrolyte contained in the cell would be degraded, which may result in the rising of the temperature and pressure within the cell and the rapid degradation of the cell. On the other hand, when the cell voltage of a certain cell is too low, the cell would be under-charged. This would certainly cause the discrepancy of efficiency and life span of respective cells in the battery array, and even cause some cells to be inefficient before the other cells.
Facing to the above-mentioned questions in the prior arts, a charging apparatus and method is desirable, which could monitor the cell voltages of the individual cells while supplying electric energy to the battery array, to regulate the charging current and charging mode for the battery array according to the result of monitoring the cell voltages. Therefore, the equalization of the cell voltages of the individual cells could be realized during the charging operation, and the over-charging or under-charging of any cells could also be avoided, thus, the life span of the whole battery array could be extended.