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Charger for 12 V starter batteries with a Schuko connection on the mains side and clamps for the battery poles
Combination battery charger with two NiCd batteries from the manufacturer Varta

A charger is a special device for recharging accumulators . The electronic circuit contained in the device, the charge regulator , controls the charging process and implements the charging process. A charger is usually supplied with power from the public power grid via a power supply unit . In model construction , mobile chargers are also common, which can optionally charge the smaller batteries of the models from a larger supply accumulator or an external power supply unit.

Often the charge controller for charging the battery is also built into the battery-operated device. Then no charger is required for charging, just a power supply unit or any suitable voltage source.


Most battery types react sensitively to deep discharge , overcharging and overheating, usually with a reduction in service life and capacity or even destruction. In addition, the charging target - a fully charged battery - may not be achieved. A long service life and full utilization of the capacity of the batteries in question can only be achieved with chargers and charging methods that are suitable for the respective battery type. The use of simple chargers, sometimes without charge controllers, requires control (e.g. time criterion) and intensive monitoring (e.g. temperature criterion) of the charging process by the user, which is practically impossible to ensure with regular use. Due to the short service life of the accumulators and constant acquisition costs for replacement, the price advantage of such "cheap chargers" is quickly consumed. The rapid development of microelectronics has increased the range of intelligent chargers in all price ranges since the 2000s. In the case of chargers for exchangeable batteries, holders for holding and making electrical contact with the batteries are often a design element; they are often referred to as charging slots. Most of the chargers are operated directly on the power grid, very powerful chargers also on the three-phase power grid .

Smaller - mostly mobile devices, for example for cell phones  - can also be charged with 12 volts, for example from cigarette lighter sockets , via solar cells or small, hand-operated generators . Since the necessary charging electronics are located in the end device, the devices and adapters required for the power supply are not chargers. Some energy sources, such as automotive alternators or solar cells, do not deliver constant power. Charging processes that require a constant energy supply, for example the detection of the gassing hump in NiMH batteries (delta peak) or simple time-controlled processes, are difficult to implement. In the case of chargers with electronic charge control, which are becoming more and more widespread, the end of charge is usually determined based on the cell voltage.


Plug-in charger with four individually regulated charging slots for 1.2 V NiMH mignon batteries
  • Plug-in charger: The charging circuit is integrated in the housing of the mains plug, usually also the charging slots. Not to be confused with a plug-in power supply unit that only provides a defined voltage or constant current. USB charger is the colloquial term for a plug-in power supply unit with a USB socket or with a cable and USB plug for devices whose USB connection is intended for charging the built-in batteries (e.g. mobile phones, digital cameras, etc.) - no charger.
  • Fast charger: The term is not precisely defined. It describes chargers that charge a battery much faster than "standard chargers", ie with higher currents. Mostly chargers with a C-factor are meant. The C-factor, the maximum charging speed, is
the ratio of maximum current to full charge and has the dimension
At C = 0.5 per hour you can half charge the battery in one hour, C = 15 per hour means that you could charge 15 batteries in one hour, i.e. 4 minutes for simple charging or discharging without using the maximum current exceed.
  • External charger: Chargers that are only connected to the device for charging, e.g. plug-in chargers or network-supported chargers for starter batteries in vehicles.
  • On-board charger: charger permanently installed in a vehicle for charging the traction battery
  • Charging slot: Holder for batteries with electrical contacts, sometimes with temperature sensors
  • Charging cradle : holder for a device with built-in batteries and electrical contacts for charging, for example for portable telephones ; with more extensive functions, often also referred to as a docking station .
  • Charging station : device at which battery systems can be charged in the installed or removed state with their own charger or a charger integrated in the station.

Charging current

The charging current describes the amperage with which a battery is charged. It is given as an absolute value in amperes , but it has also become established in battery technology to specify the current for charging and also for discharging in relation to the capacity of the battery in ampere-hours (Ah) in order to describe the load on the battery (see also Peukert equation ). A battery with a capacity of one ampere hour that is charged with a charging current of two amps is charged at 2C, i.e. twice the capacity. If the charging current is lower, a ratio to the capacity is specified, for example C / 2 for 0.5 A (specification of 0.5C is also common) in the above example. The indication as a fraction is justified insofar as the time in which the nominal capacity is charged or discharged can be clearly recognized: At C / 2 it is 2 hours. For lead-acid batteries, the specification of the nominal capacity at C / 20, i.e. a discharge of over 20 hours, is common, with other battery types, depending on the field of application, shorter times are also common.


All chargers should recharge an accumulator for mobile operation of electrical devices after discharge. The design varies considerably depending on the intended use and battery type.

Simple chargers

Charger without mains disconnection for button cells of the transistor radio Kosmos (approx. 1969)

Chargers often consist of a separate plug- in  power supply and a charging circuit housed in the device near the battery - in this case the plug-in power supply only supplies the transformed, but otherwise unregulated voltage . This is particularly common with lithium-ion batteries , as their end-of-charge voltage and temperature cannot otherwise be measured precisely enough. The plug-in power supply transforms the mains voltage to a lower AC or DC voltage , for example to 9  volts .

Simple chargers charge a battery with constant current (e.g. nickel-cadmium batteries ) or constant voltage (e.g. lead-acid batteries ). They do not have any other devices for controlling, monitoring and terminating the charging process and occasionally have a time-controlled shutdown device. The charging time and charging current are specified for many batteries so that charging can only be carried out approximately correctly if the state of discharge is known. However, this assessment must be made by the operator. Incorrect assessments lead to overcharging or not fully charged batteries. Failure to switch it off can also result in overcharging of the batteries, since human actions can also be assumed to be incorrect operation (e.g. forgetting). Fast charging and charge status monitoring are not possible with this device type.

Seen over many charging processes, this destroys the electrochemical system in the battery and makes the cell unusable. The cells lose their capacity and are no longer resilient. Massive overcharging can cause gas to build up inside the battery. If it becomes too big, it triggers a safety valve so that gases and electrolyte escape. This is a safety function to protect the battery from bursting.

With pair chargers, two cells connected in series are charged equally. They are only intended for cells that are also used in pairs. If these two cells differ in their charging status, the full battery will be overcharged for a long time or the empty battery will not be fully charged (see balancer ). In some cases, the charger no longer correctly recognizes the end of charging if the charging electronics are equipped with the appropriate equipment, which means that both cells are then overcharged if further safety measures such as a time-controlled shutdown or temperature monitoring do not end the charging process.

Electronic chargers

Electronic chargers - often referred to as intelligent - have more complex electronic charging circuits or a built-in microcontroller and can therefore implement more complex charging processes adapted to the type of battery. An exact detection of the full charge of the connected battery due to the gassing hump (see charging procedure ) allows safe fast charging without the risk of overcharging, which shortens the life of the battery. Further properties are, for example, the automatic discharge of the batteries before the start of charging or loading programs to regenerate by repeatedly charging and discharging the cell, the automatic switch to trickle charge after the end of charge and the variation of the charging currents and the monitoring thereof with reference to the temperature ( temperature compensation ).

Intelligent chargers for individual cells have individual shaft monitoring. It monitors the cell voltage and often the cell temperature of each battery cell individually. Some devices can also determine the capacity via charge and discharge programs. This makes it easy to identify worn or defective cells. Independent charging of the individual cells avoids overcharging individual cells or not charging them completely, as can occur with battery packs or multiple chargers. It is also a form of manual balancing .

Chargers for battery packs are often able to determine the number of cells themselves and to adjust the charging parameters accordingly. Lithium high-performance battery packs for model making always have individual monitoring of the cells, corresponding chargers are matched to this.

Sometimes the charging electronics are integrated in the battery itself, for example in mobile power storage devices such as those offered for USB devices. Batteries that are permanently adapted to specific devices, such as the lithium-ion batteries used in cell phones and portable computers, usually only have an internal protective circuit that switches off in the event of excess temperature, short circuit , undervoltage or overvoltage. As a pure safety element, it does not fulfill the function of a charge controller. Furthermore, these batteries often contain separately brought out temperature sensors with which the charging circuit monitors the temperature limits and evaluates the charging efficiency .

In RC model making, lithium battery chargers often have integrated balancers .

Alternative charging technology

Mobile power sources

The increasing performance of modern smartphones and tablets and the trend towards ever thinner housings has meant that the operating time with the integrated batteries can sometimes shrink to less than two hours with intensive use. There are not alternatively usable batteries with extended capacity for every model, which has led to the development of a diverse range of external, transportable power supplies.

Power bank

Example of a power bank

Powerbank is the slang term for a mobile additional battery, not a charger.

Solar modules with charge regulator

Foldable solar module with 7 Wp and mobile phone with USB charging connection

In the portable sector, especially for devices that are charged via the USB interface , but also for single cells (especially AA and AAA), there are various solar chargers that are intended to meet the need for regenerative and mobile energy.

While even small solar cell surfaces are sufficient for devices with low energy requirements, for example radios or clocks, significantly larger surfaces are required to charge mobile phones or mignon cells. Often, short loading times are expected even in poor sunlight (e.g. behind windows). Devices with small solar cells, which are often only the size of a smartphone, usually cannot meet this expectation. They are only able to deliver a relevant charging current under optimal conditions. In the case of integrated rechargeable batteries, the problem is that the devices have to be positioned in blazing sunlight. The entire device including the battery heats up strongly, which is detrimental to the battery life.

In the case of pure solar modules without buffering, the performance drops sharply even with light, brief shading. If devices are charged with electronic detection of the voltage supply, this leads to the termination of the charging process, which then does not necessarily continue automatically depending on the device. Here, however, there are special buffer batteries with an integrated solar charge controller or simple external USB batteries that can be positioned in the shadow of the solar module. However, only a few of the latter devices can be charged at the same time via the solar module while they are delivering energy to the end device.

Qi charging technology

Qi logo

A new development in the field of charging adapters is Qi charging technology, which uses the Qi standard . The energy is transmitted inductively, which represents a gain in convenience compared to cable-based plug connections and increases reliability because there are no wearing plug contacts. This cross-device standard was developed by the Wireless Power Consortium and is currently mainly aimed at smartphones. Theoretically, any small device could be equipped accordingly and thus charged wirelessly.

In order for a device to be able to use the Qi standard, a corresponding Qi transmitter and Qi receiver are required. Some smartphones, such as the Google Nexus , contain an internal receiver module. External Qi receivers with a micro-USB connection can be used for smartphones from various manufacturers . Modules for proprietary connections such as the Apple iPhone are also available. The advantage of being plugless is lost again with external receivers.

The Qi charging technology has a lower efficiency than conventional chargers (efficiency of approx. 0.6) due to the losses in inductive energy transmission. This is offset by the increased convenience associated with wireless technology. Qi transmitters are partially equipped with a USB connection and can therefore also be supplied with the existing USB plug-in power supply. The charging speed depends on the power profile according to the QI standard. A distinction is made between the "Baseline Power Profile", which transmits up to 5 watts, and the "Extended Power Profile", which transmits up to 15 watts. In the case of passive quick chargers with the "Extended Power Profile", which are often supplied via a USB power supply unit, the quick charging function can only be used if the connected USB power supply unit provides sufficient energy. Furthermore, the recipient must support the rapid charging capability via the QI standard. Depending on the possible performance, depending on the device, charging times may be longer than with wired chargers.

Charge regulator in motor vehicles

Starter batteries in motor vehicles are charged with a charge regulator via the alternator while the engine is running . The charge regulator controls the excitation current of the alternator in order to regulate the charging voltage (13.8 to 14.2 volts for a 12-volt on-board network) and to recharge the on-board accumulator, independent of load and speed.


  • Ulrich Passern: Batteries & chargers for model sports: Basics, charging techniques, practical tips. (with CD-ROM ). vth, Baden-Baden 2004, ISBN 3-88180-736-5 .
  • Ludwig Retzbach: Batteries and chargers. 14th edition Neckar, Villingen-Schwenningen 2008, ISBN 978-3-7883-4142-8 .
  • Thomas Riegler: Batteries and chargers. vth, Baden-Baden 2009, ISBN 978-3-88180-785-2 .

Web links

Commons : Chargers  - collection of pictures, videos and audio files
Wiktionary: Charger  - explanations of meanings, word origins, synonyms, translations