During a capacity test or a heavy discharge, increased heat generation may occur at connectors or disconnecting devices. One reason for this may be a high transition resistance due to incorrectly tightened pole screws. Increased gassing of a single battery in the overall system can also be determined by temperature development, so that a possible defect can be detected early and action taken accordingly. The measurement is carried out with certified measuring instruments so that even the smallest thermal deviations can be detected and eliminated. The scope of services can be combined with any other service product in order to make as accurate a statement as possible about the test object in question.