Short circuit, over-charge, and over-heat protection,very safe. After fully charged one time, can keep about months.Noraml use can keep 3-5years. Start car at one time on cold & hot areas. Very connvenient.can be charge at home(100-240V) and car.Normally use 3hours for full charge. By using our free connector ,you can use it to provide power for your car refrigerator or other 12V electronics like car cleaner. Safety hammer for knock glass when meet emergency.