This is a 4 Bank Lithium & AGM Marine Battery Charger perfect for charging 1 AGM cranking battery & (3) 12v LiFePO4 batteries. This charger has built in low voltage cut off charging activation with a push of a button. This means when you run your lithium batteries all the way down they will reach what is called low voltage cut off, when this is reached the BMS (battery management system) basically turns the battery off at this point showing zero to little voltage to where the charger doesn't recognize that there is a battery connected. The activation button adds a short pulse charge into the battery waking up the BMS and allowing charge to start entering the battery. The AGM lead does not have the activation button as it does not contain a BMS and therefore does not have a low voltage cut off mechanism. This charger is 100% waterproof!