The battery charger/maintainer has been designed to work with both 6V and 12V batteries. The unit is designed to maintain charge on both large and small batteries. It is not recommended to use this charger/maintainer to solely charge a large battery, as it can adversely affect the battery’s capability to hold a charge. The maintain mode does allow you to maintain battery charge for extended periods of time, but remember that improper connections, vehicle electrical problems and other conditions can cause unexpected current draw. Always monitor the battery and the charging/maintaining process.