A universal battery charger is a type of battery charger designed to charge or recharge any type of battery, including various sizes as well as types of battery, like nickel-cadmium, alkaline, and others. No single battery charger can charge every type of battery in existence, so several types of universal battery charger exist. The type most commonly referred to as a universal charger will charge any type and any size of common household battery. Charging pads will charge any device capable of inductive charging.
The term universal battery charger is a little misleading. Several types of universal battery chargers exist, but none of them can charge every kind of battery. The term really means that a given universal battery charger will charge all of a certain range of batteries. One type will charge almost any common household battery, another type will charge almost any type of cell phone, and yet another will charge almost any type of industrial battery. Each is universal in a limited sense, as a universal battery charger for household batteries will most likely not work for charging cell phones or other similar devices.
A smart charger is a type of universal battery charger that can detect the charge present in a battery and analyze the battery to determine the optimum charge rate and maximum charge. This is the closest thing to a truly universal charger. These types of chargers are usually very expensive and are sometimes used by various militaries and airlines for charging aviation batteries and other sophisticated batteries whose applications are of top importance.
One popular type of universal battery charger is a charging pad. Several brands of this device are available on the market, and allow any digital device equipped with an industry charging standard called Qi to be charged simply by placing the device on the charging pad. These use a new technology called inductive charging to charge a device by means of electromagnetic fields, without the need for exposed metal contacts. Any device with inductive charging capability can be charged by a charger of this type, including phones, tablet computers, music players, and many others. This technology was originally developed for use with devices like rechargeable toothbrushes and other devices that might be used around water to eliminate the risk of electrocution due to water coming in contact with bare metal electrical contacts.