When mix use batteries of different capacities and different voltages, leakage or short circuit may occur. These problems occurred because some of the batteries will be over charged and some others are not charged to full capacity. When these batteries are discharged together, the batteries with full capacity cannot be fully discharged while the other batteries with low capacity will be over discharged. In this way, the batteries will be damaged and leakage or short circuit low (zero ) voltage will occur.