The USB in-car charger is a very simple piece of equipment to use. Simply plug it into your cigarette lighter port in your car, and then insert a USB cable to charge your battery.
Your car battery must be switched on in order to charge your battery through the USB Car Charger.
Be careful not to use short-journey recharges too often, as it can damage your battery life (reduces the life expectency). This is because most batteries have a 300 charge lifetime. Each time it is activated, one of those charges is lost. Therefore car-charging is more suited for long journeys or emergency boosts only!