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A battery charger is a device used to put energy into a cell or (rechargeable) battery by forcing an electric current through it.
The charge current depends upon the technology and capacity of the battery being charged. For example, the current that should be applied to recharge a 12 V car battery will be very different to the current for a mobile phone battery.
Additional recommended knowledge
Types of battery chargers
A simple charger works by connecting a constant DC power source to the battery being charged. The simple charger does not alter its output based on time or the charge on the battery. This simplicity means that a simple charger is inexpensive, but there is a tradeoff in quality. Typically, a simple charger takes longer to charge a battery to prevent severe over-charging. Even so, a battery left in a simple charger for too long will be weakened or destroyed due to over-charging.
The output of a timer charger is terminated after a pre-determined time. Timer chargers were the most common type for high-capacity Ni-Cd cells in the late 1990s for example (low-capacity consumer Ni-Cd cells were typically charged with a simple charger).
Often a timer charger and set of batteries could be bought as a bundle and the charger time was set to suit those batteries. If batteries of lower capacity were charged then they would be overcharged, and if batteries of higher capacity were charged they would be only partly charged. With the trend for battery technology to increase capacity year on year, an old timer charger would only partly charge the newer batteries.
Timer based chargers also had the drawback that charging batteries that were not fully discharged, even if those batteries were of the correct capacity for the particular timed charger, would result in over-charging.
Output current depends upon the battery's state. An intelligent charger may monitor the battery's voltage, temperature and/or time under charge to determine the optimum charge current at that instant. Charging is terminated when a combination of the voltage, temperature and/or time indicates that the battery is fully charged.
For Ni-Cd and NiMH batteries, the voltage across the battery increases slowly during the charging process, until the battery is fully charged. After that, the voltage decreases, which indicates to an intelligent charger that the battery is fully charged. Such chargers are often labeled as a ΔV, or "delta-V," charger, indicating that they monitor the voltage change.
Fast chargers make use of control circuitry in the batteries being charged to rapidly charge the batteries without damaging the cells' elements. Most such chargers have a cooling fan to help keep the temperature of the cells under control. Most are also capable of acting as a standard overnight charger if used with standard NiMH cells that do not have the special control circuitry. Some fast chargers, such as those made by Energizer, can fast-charge any NiMH battery even if it does not have the control circuit.
Some chargers use Pulse technology in which a pulse is fed to the battery. This DC pulse has a strictly controlled rise time, shape, pulse width, frequency and amplitude. This technology is said to work with any size, voltage, capacity or chemistry of batteries, including automotive and valve-regulated batteries.
Since the Universal Serial Bus specification provides for a five-volt power supply, it's possible to use a USB cable as a power source for recharging batteries. Products based on this approach include chargers designed to charge standard NiMH cells, and custom NiMH batteries with built-in USB plugs and circuitry which eliminate the need for a separate charger.
Since a battery charger is intended to be connected to a battery, it may not have voltage regulation or filtering of the DC voltage ouput. Battery chargers equipped with both voltage regulation and filtering may be identified as battery eliminators.
Mobile phone charger
Most mobile phone chargers are not really chargers, only power sources for the charging circuitry which is almost always contained within the mobile phone. Mobile phones can usually accept relatively wide range of voltages, as long as it is sufficiently above the phone battery's voltage. However, if the voltage is too high, it can damage the phone. Mostly, the voltage is 5 volts or slightly higher, but it can sometimes vary up to 12 volts when the power source is not loaded.
Battery chargers for mobile phones and other devices are notable in that they come in a wide variety of connector-styles and voltages, most of which are not compatible with other manufactuers' phones or even different models of phones from a single manufacturer.
Users of publicly accessible charging kiosks must be able to cross-reference connectors with device brands/models and individual charge parameters and thus ensure delivery of the correct charge for their mobile device. A database-driven system is one solution, and is being incorporated into some of the latest designs of charging kiosks.
A travel charger from Ionhub is a portable charging hub.  It is more of a universal charger because it can simultaneously charge many different electronic devices.
There are also human-powered chargers sold on the market, which typically consists of a dynamo powered by a hand crank and extension cords. There are also solar chargers.
China and other countries are making a national standard on mobile phone chargers using the USB standard.
Battery charger for vehicles
There are two main types of charges for vehicles:
Battery electric vehicle
These vehicles include a battery pack, so generally use series charger.
If your battery system is 9kWh or kilowatt-hours and the charger used by you is 1 kilowatt (kw), it could take 9 hours (9hrs * 1kW = 9kWh) to fully charge the battery. 
The chargers used in electric vehicles can be:
Power Factor Correction (PFC) chargers can more closely approach the maximum current the plug can deliver, shortening charging time.
Some battery electric vehicle charging devices includes:
Project Better Place is going to deploy a network of charge stations. It also subsidize vehicle battery costs through leases and credits.
Prolonging battery life
Many rumors circulate about the best practices to prolong battery life. What practices are best depend on the type of battery. The older nickel-based batteries are harmed by charging them when not full, which explains the preponderance of rumors.
Most modern cell phones and laptops use Lithium-ion batteries. Contrary to some recommendations, these batteries actually last longest if the battery is not fully discharged. Deterioration occurs faster at higher temperatures. Lithium batteries deteriorate more while fully charged than if it is only 40% charged. The conditions of high temperature combined with full charge are exactly the scenario occurring when a laptop computer is run on AC power. Deterioration is caused by resistance due to oxidation and thus affects usage that draws more current.
The "digital memory" exhibited by many rechargeable batteries does not actually affect battery life; instead, it is caused by a failure of the gauge to calibrate properly in the absence of a full discharge. Fully discharging the battery once every 30 charges can remedy this problem; a full discharge each time is neither necessary nor beneficial to the battery.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Battery_charger". A list of authors is available in Wikipedia.|