WET CELL BATTERIES should be filled to within how many inches of the top of the filler plug?

Wet cell batteries should be filled to within 1/4 inch of the top of the filler plug to ensure proper operation and performance. This specific distance is critical because it allows for adequate expansion of the electrolyte during changes in temperature and prevents overflow, which could lead to corrosive damage or short-circuiting. Additionally, maintaining this proper level helps to ensure adequate contact between the plates and the electrolyte, which is essential for the battery's efficiency and longevity. Filling beyond this level may increase the risk of electrolyte spillage, while filling below it could lead to inadequate performance and potential damage to the battery.