The iButton temperature logger is a robust and independent system that measures temperature and records the temperature data in a non-volatile memory section. Although iButtons are a relatively mature product, failures due to Battery Depletion and Battery-On-Reset (BOR) occur. Despite the implementation of major corrective actions to improve product reliability and robustness, customer failures due to Depleted Battery and BOR have not been fully eliminated. One recent quality issue involved a high failure rate on one iButton variant at the customer’s quality control before calibration, which prompted a thorough failure analysis to nail down the real cause of failure. This paper presents methodical failure analysis (FA) steps and processes that led to the identification of failure mechanisms. As a result, the real issue was detected leading to a more accurate corrective action and device reliability.