The most important terms concerning electromobility

E-Mobility Glossary

  • Knowledge, Charging, Corporate, Technical, Private, Business
From the outside, a conventional combustion engine differs only marginally from its electric relative - internally, however, it differs a great deal. A different engine brings with it many new terms that require explanation. From 'A' as in 'AC' to 'F' as in 'FI circuit breaker' and many other terms, we have listed the most important technical vocabulary that an e-car driver should know.

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

Our glossary is regularly updated with new terms. So it's worth checking back here from time to time!



AC is short for ‚alternating current ‘. In alternating current, the direction in which the electrons flow—the polarity—changes fifty times per second. The public power grid uses AC, as it allows for a low-loss voltage change, which is an advantage for transporting electricity across long distances. So, the home socket provides alternating current. The battery of an electric vehicle, however, requires direct current (DC). That’s why each EV has a rectifier installed that converts AC into DC when charging at AC charging stations such as a wallbox. If energy is taken out of the battery, an inverter converts DC back into AC, as the electric motor requires it.


Battery Capacity

The battery capacity is the storage capability of a battery. The battery is the equivalent of the fuel tank of a vehicle with a combustion engine. The higher its capacity, the further you can drive with comparable consumption. It’s important to differentiate between gross and net capacity. Unlike the fuel tank, a battery cannot be fully emptied; a certain percentage remains unused. Net capacity describes the usable capacity, gross capacity the theoretical capacity. An electric vehicle’s battery dimension—like with energy consumption—is measured in kilowatt hours (kWh). For instance, if an e-car consumes 15 kWh per 100 km, a battery with net 50 kWh will take you about 330 km. If the battery capacity is at net 75 kWh, a distance of 500 km is possible with a fully charged vehicle.


BEV is short for ‚battery electric vehicle‘. When we talk about these vehicles, we often only say ‚EV‘ (electric vehicle). Strictly speaking, this is incorrect. Because EV is the umbrella term for all vehicles with an electric power system, from e-scooters to fuel cell electric vehicles (FCEVs). The difference is in the way they store energy. While most EVs now use a battery as their storage medium (BEVs), vehicles with fuel cells use hydrogen or methanol. What all EVs have in common is that they are powered by a purely electric system with one or more electric motors—some are fed with electricity from batteries, while others use tanks and a fuel cell that generates electric energy on board.

Bidirectional charging / Bidi charging

Bidirectional charging generally means the use of the vehicle battery for external consumers. The energy stored there feeds not only the electric motor and the usual car equipment but also e.g. a vacuum cleaner or refrigerator. It is also technically possible to supply the entire building with electricity. Theoretically, bidirectional charging can go as far as using the electric vehicle’s battery as a system buffer. In that case, electricity from the grid is stored in the vehicle battery during peak production and fed back into the grid during peak consumption. This reduces the grid’s load and makes for a better use of electricity from renewable sources.



Calibration is the legally prescribed testing of a measuring instrument for compliance with calibration-act guidelines, in particular the calibration error limits. In order to legally pass on electricity charging costs to customers, tenants, or employers (in case the company vehicle is charged at home), a calibrated meter must record the electricity that has been charged. In theory, this is possible with a separate energy meter connected upstream of the charging station. This solution, however, is complex and expensive and cannot record the consumption for individual charging sessions in isolation. Wallboxes with an integrated calibrated meter are the simpler solution. In Europe, an MID-certified meter is usually sufficient, but in Germany, the meter must comply to the stricter requirements of the national gauging and calibration act. Devices with this type of calibration are marked with the acronym ME for Mess- und Eichrecht, often visible from the outside.


CCS is short for ‚combined charging system‘, which describes the connector standard or the plug system of modern e-cars. CCS allows for charging with both alternating current (AC) via a Type 2 connector at home or at work and direct current (DC) with higher charging rates at compatible fast-charging stations. The combined inlet consists of a top inlet for Type 2 connectors with a maximum of five contacts for 3-phase alternating current charging as well as two signal pins and a bottom connector with two contacts for direct current charging. Currently, the CCS system allows AC charging of up to 22 kW and DC charging of up to 350 kW.

Charging Power

Charging power is an important factor for the charging speed. Mainly limiting the charging power, along with various external factors like outside temperature, charge level, and the charging station’s power, are the battery’s constant internal factors (size, cell chemistry, and architecture) as well as the charging management. Ideally, the limiting component is always the vehicle. So, the charging power of e.g. an e-scooter is only a few kilowatts, while other e-vehicles are able to handle the power of more than 300 kW. Since a battery can never be continuously charged with high power, these figures are maximum values—a peak performance that can only be held over a few short minutes. What’s more significant is the average charging power, especially at a state of charge (SoC) between 10 and 80 percent. In practice, however, the loading system is often a power limiter. The power (P) is the product of electric current (I) and voltage (U). A domestic wallbox with a 3-phase plug therefore has a maximum output of 16 A × 3 × 230 V = 11 kW. This is sufficient for charging overnight and preserves battery life. DC fast chargers, on the other hand, can generate power of up to 400 kW in theory (500 A × 800 V) and are therefore the best choice when it comes to travelling long distances.


Direct Current

Direct current (DC) is when the electrons flow in one direction only. Batteries deliver direct current, and so do photovoltaic systems. If consumers are plugged in, the electrons travel from the anode (minus) to the cathode (plus). The public power grid, however, operates with alternating current (AC), as it allows for a low-loss voltage change. This is why a rectifier is needed when charging electric vehicles with alternating current, for instance via a wallbox at home. The rectifier turns alternating current into direct current, AC into DC. Every e-car has one. If energy is drawn from the battery, an inverter converts DC back into AC, as the electric motor requires it.


DC is short for ‚direct current‘. Directly above you can find out what DC means.


Energy Meter

An energy meter measures the electricity that flows through it. So, it detects power that is generated, for instance by a PV system, as well as the consumption, for instance at home. In contrast to a regular electricity meter, an energy meter is an electronic sensor. The term often describes the smart version of an electricity meter, capable of communicating with other components, such as the wallbox. An energy meter in this modern sense is definitely needed if one wishes to optimise the energy management of a building.


FI Circuit Breaker / FI-protection switch

‘FI circuit breaker’ or ‘FI-protection switch’ are still common terms for a protective device that interrupts the circuit in the event of a fault current. F stands for 'fault', I for the physical unit of the current intensity.  In the meantime, one speaks of a residual current device, abbreviated as RCD (for 'Residual Current Device').  The RCD detects if something is being lost in a current circuit. In a closed circuit this may not be the case. Thus it protects humans (and animals) from being exposed to large currents permanently. If, for example, current is dissipated through the body by contact with a conductor, a so-called differential current is generated. If this is too large - the maximum value is specified on the RCD as In - the circuit breaker interrupts. All KEBA wallboxes are equipped with DC leakage detection. This significantly reduces the costs of the installation, since only one type A RCD needs to be installed instead of an expensive type B RCD.


Gauging and calibration act (Mess- und Eichrecht, ME)

The so-called gauging and calibration act (Mess- und Eichrecht, ME) is the German implementation of the European directive for the calibration of measuring devices (MID). Charging stations that are compliant to these gauging and calibration standards tend to be a bit more expensive than MID-certified ones, as they require more complex hardware. Unlike wallboxes with uncalibrated or MID-certified meters, ME-compliant devices must store information about individual charging sessions in the charging station itself and over a longer period of time.


Kilowatt (kW) 

W stands for ‚watt‘, the unit with which to measure the physical quantity of power (P). While a dustbuster might need 700 W, much higher power is required to drive a car. To keep the figures manageable, we use the unit kilowatt (kW), which is equal to 1,000 watts (≙ 1.36 hp). Two power categories are important for battery electric vehicles: the driving power (the engine power) and the charging power, which is an essential factor when talking about charging speed. The maximum theoretical charging power is limited by the charging station’s output (in a domestic socket that’s only 10A × 230V = 2.3 kW) as well as the battery or the vehicle’s own charge management. The limits diverge wildly and range from a few kilowatts to more than 300 kW.

Kilowatt hour (kWh) 

Wh stands for ‚watt-hour‘, the unit with which to measure how much energy a system consumes or gives off per hour with the power of one watt. In the context of battery electric vehicles, it is used mainly to indicate the battery capacity. To keep the figures small, we use kWh (=1,000 Wh) instead of Wh. A battery with a capacity of 50 kWh is capable of giving off the power of one kilowatt for fifty hours. This is a theoretical value, as the engines especially of electric cars release far greater power—when accelerating over short periods of time this could be several hundred kW, depending on the vehicle type. Yet the theoretical value illustrates well how a battery with twice the capacity can also give off energy for twice as long and can thus also store twice as much energy.


Measuring Instruments Directive (MID)

The Measuring Instruments Directive (MID) is an EU guideline specifying the requirements of measuring instruments. With the introduction of the MID, calibration in state-approved testing centers has been replaced by the manufacturer’s declaration of conformity. The calibration’s validity period continues to be based on national regulations. Only MID-certified energy meters may be used for billing electricity costs - with the exception of Germany and, since March 2022, Austria, where stricter requirements must be met, and the energy meter must comply to the standards put forth in the country’s gauging and calibration act (ME).



RCCB is short for ‚residual-current circuit breaker‘, which is still often called by its older term RCD (residual-current device). It is a safety device that breaks an electrical circuit in which leakage current has been detected. The RCCB identifies a loss in the electrical circuit. In a closed circuit, loss is impossible. And so, the RCCB protects people (and animals) from long exposure to high currents. If a person touches a conductor and electricity discharges into the body, it leads to so-called “residual current.” If it is too high—the maximum value is noted on the switch as In—the switch breaks the circuit. All KEBA wallboxes are equipped with DC leakage detection. This reduces the installation costs considerably, as it requires only a Type-A switch instead of the expensive Type-B RCCB.


Vehicle-to-Load (V2L)

Vehicle-to-Load is a special form of bidirectional charging. It means using the energy stored in the electric vehicle to supply external consumers like vacuum cleaners, saws, etc. Because of its diversity of use, we also call it Vehicle-to-Utility. The electric car serves as a large power bank of sorts for electrical devices. The energy is taken either from the power outlet or via an adapter plugged into the connector.

Vehicle-to-Vehicle (V2V)

Vehicle-to-Vehicle refers to a special form of bidirectional charging. It refers to the extraction of energy from one electric vehicle’s battery to charge another. The electric car functions as a charging station to supply other vehicles that are low on battery with electricity.

Vehicle-to-Home (V2H) / Vehicle-to-Building (V2B)

Vehicle-to-Home is a special form of bidirectional charging. It refers to the use of the energy stored in an electric vehicle’s battery for consumers within an apartment or single-family home. The electric car thus supplies a household with electricity. In this way, self-produced electricity, e.g. from your own PV system, can store electricity in times of low demand and high production rates for later use. This makes you less dependent on grid electricity, can lower consumption costs, and helps to reduce grid load. If the batteries of more than one car are used to supply larger buildings with energy, we call this Vehicle-to-Building. It works the same, but consumption and storage capacity are scaled.

Vehicle-to-Grid (V2G)

Vehicle-to-Grid is a special form of bidirectional charging. It refers to the use of energy in an electric vehicle’s battery as buffer storage for the entire grid. In this way, electricity can be stored during periods of low demand and high production rates for later use. On one hand, this increases the use rate of electric energy from regenerative sources such as PV and wind energy, which only occurs temporarily. On the other, it helps this technology to reduce grid load. The use of existing storage capacities in electric cars also reduces the need for large, invasive and expensive storage systems such as pumped storage.


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