A battery tester capable of measuring resistance and voltage of a battery using the same input channel. When measuring battery resistance, a testing signal circuit is electrically coupled to two electrodes of a subject battery to conduct a testing signal used in the battery resistance measurement. A response sensing circuit of the battery tester is also electrically coupled to the two electrodes of the subject battery to measure a response signal across the two electrodes of the subject battery. A resistance measuring module is electrically coupled to the response sensing circuit to measure the battery resistance based on the response signal detected by the response sensing circuit. A circuit breaker is capable of disconnecting the subject battery from the testing signal circuit, and disconnecting the resistance measuring module from the response sensing circuit. Moreover, the battery tester can also provide automatic protection for the battery resistance measuring module.