The "ZC-N" battery internal resistance tester adopts the improved DC test method, automatically selects the test current according to the capacity of the battery to perform short-time constant current discharge on the battery, and collects the battery voltage at high speed, and then performs digital filtering and precision calculations according to the internal resistance characteristic to get the DC internal resistance value. Meanwhile, the connecting resistance between the batteries can be measured. This method has accurate measurement results and good retestability. The test data can be automatically saved without power loss, and the test records saved can be downloaded through USB. The background software is used to analyze and process the data and to generate various forms of reports such as data tables and histograms. This product is small in size, light in weight and easy to carry, which can be widely used in battery rapid detection, daily maintenance and installation acceptance of battery pack.