Honda Civic battery dying overnight despite checking alternator and other components on Honda Civic

Some Honda Civic owners report experiencing battery drain issues overnight, often attributed to key-off drain, also known as parasitic drain, which occurs when something in the vehicle continues to draw power even when turned off. Others have identified a malfunctioning alternator as a potential cause, as it is responsible for charging the battery while the car is running; if it fails, the battery may not charge adequately. Additionally, some owners find that a dead cell in the battery itself can lead to similar problems, regardless of the alternator's functionality. It is recommended that owners conduct parasitic draw testing to identify any abnormal power draws when the vehicle is off, especially if the alternator and starter are confirmed to be working properly. Moreover, those who do not drive their cars frequently are advised to start the vehicle for a few minutes daily to help maintain battery charge. Lastly, if the car can be jump-started and continues to run, it suggests that the alternator may still be partially operational, which can help diagnose the source of the battery drain issue.