1.the root cause is related to poor sealing of two of tiny batteries and end up batteries was rusted. Would like your QA to explain in details the consequence:
Poor Sealing -> allow air to have chemical reaction with anode/cathode chemicals ? -> the tiny batteries conductive part got rusted ? -> What is the impact of rusted part on performance of batteries -> etc.
2, And for the preventive actions parts, please explain in details the process / materials change involved.
Improve Sealing -> which part ? -> How is this done ?
Improve visual inspection to reject faulty units -> actions involved ?