Efest LUC Blu4 LCD Intelligent Bluetooth Charger For 18650 Batteries Intelligent lithium ion battery charger with Bluetooth connectivity Compatible with most sizes of cylindrical lithium-ion batteries ranging from 10440 to 18650 Automatically detects battery power status and selects the appropriate voltage and charge mode Automatically stops when charging is complete and prevents batteries from being over-charged Features reverse polarity protection if you accidentally insert a battery the wrong way.