A car charger is a device that plugs into the 12-volt cigarette lighter outlet inside a vehicle, then connects to an electronic device such as a cell phone or MP3 player to charge the battery. The cell phone will typically connect to the car charger through a USB port or simple power cord. Though there are many "universal" car chargers available, unfortunately many cell phones use a proprietary design, and it is often necessary to purchase a new car charger with every new cell phone.
It is possible, of course, to talk on the phone while it is still plugged in to the car charger. However, some experts advise against doing this too frequently, as it can affect the life of the battery. In general, it is best to allow the cell phone's battery to drain as much as possible before plugging it in again; do not simply plug the cell phone into the car charger every time it is in the vehicle. Allow the battery to fully charge each time before using it to get the most life out of the battery.
Car chargers are typically not meant to be the sole method of charging the battery of any device. It is best to only use a car charger when needed, but in general, charge devices by plugging them into the wall. The documentation that comes with any device will specify the amount of charging cycles that can be expected with each individual type of battery before it will need to be replaced.
Some types of car chargers have dual purposes. One popular type works as a battery charger as well as an FM transmitter, and is a popular choice for MP3 players or phones that can play music. The charger will charge the battery of the device while broadcasting the music over one of the FM channels on the radio in the car, as selected by the user.
Car chargers can be found in virtually any electronics store or cell phone retailer. They are typically fairly inexpensive, and are a good idea to keep in the car in case of an emergency. In addition to car chargers that plug into the cigarette lighter outlet, newer types of chargers are now being sold. These include solar chargers as well as manual chargers, which feature a hand crank that the user can turn to charge the cell phone's battery.
Car chargers exist for laptops as well, but these are typically much larger as they require a power adapter to convert the vehicle's power supply to match the laptop. It is almost always necessary to purchase a proprietary brand of laptop car charger for the specific brand of laptop owned. These types of chargers should also not be used as the primary method of charging a computer.