If you're going to leave your car idling for too long, sooner or later, the battery will die completely. To avoid it depleting fully, it's a good idea to hook up your car to a battery charger to maintain its charge. Battery chargers essentially trickle in small currents at a time to keep the battery topped up when you need it. To charge a battery, a good first step would be accessing the battery. Then, ensure that all in-car electronics are turned off. Once you're ready, grab the battery charger. Now, connect the positive lead to the battery first, followed by the negative lead. This is crucial, as you need to follow this order - positive first, then negative. When that's done, plug the battery charger into a wall outlet, and turn the device on to charge your car's battery.