Printed Circuit Boards used in outdoor and forest environments face serious challenges due to harsh conditions, which can lead to early failure even when they are protected with conformal coatings. This study tested three common types of coatings: polyurethane, synthetic rubber, and ultraviolet curable acrylate. These were applied to both standard IPC-circuit boards and complex battery management system boards. The coatings were tested under different stress conditions, including humidity, salt fog, thermal shock, and contamination. The results showed that full coverage, especially on sharp edges and complex areas, is very important for protection. Some coatings broke down faster when exposed to several stress conditions at the same time. Synthetic rubber showed more stable results in many of these cases. The study recommends using combined stress tests for a higher reliability, instead of only one type of test and offers a test scheme to guide practitioners in their evaluation. In doing so, circuit boards can become more reliable in outdoor environments.