Abstract: The present invention discloses a battery tester having high precision, which has a casing having an input device and two detecting wires, a microprocessor, a variable loading unit and a battery power status detecting unit. The microprocessor builds a strategic decision process therein to determine a proper resistance of a load for a battery according to the battery capacity, initial voltage and detection requirements having 1/N CCA and loading time. When the resistance of the load is determined, the microprocessor adjusts a resistance of the variable loading unit equal to the resistance of the load for the battery. Therefore, the battery tester does not use the load with the fixed resistance to detect batteries with different capacities and has accurate detecting results.