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Battery Charger Comparison
From the chargers listed there, I have TurboCharger 4000 and am very pleased. It has a thermal switch that terminates the charging if the batteries begin to heat up. There are other smart charger options there, including the possibility to charge an odd number of cells. Simple chargers either take forever to charge or fry the batteries. I would not charge a set where one battery is dead - either the other will not charge or you will have a good chance to damage the other as well.