Method and apparatus for diagnosing battery system

A method for diagnosing a battery system having a hierarchical structure including a lower-level battery device and a higher-level battery device, the method comprising:

• determining, by a processor, first and second charge/discharge test environments providing complementary characteristics for performance degradation of the higher-level battery device exhibits by performing a charge/discharge test with respect to the higher-level battery device;
• performing, by the processor, a charge/discharge test with respect to the lower-level battery device under the first and second charge/discharge test environments to determine whether a test result matches the complementary characteristics under the first and second charge/discharge test environments;
• and
• deriving, by the processor, optimal operating conditions of the battery system in which the complementary characteristics under the first and second charge/discharge test environments are removed, upon determining that the test result of the charge/discharge test with respect to the lower-level battery device matches the complementary characteristics under the first and second charge/discharge test environments.