A battery indicator (also known as a battery gauge) is a device which gives information about a

battery Battery most often refers to: * Electric battery, a device that provides electrical power * Battery (crime), a crime involving unlawful physical contact Battery may also refer to: Energy source *Automotive battery, a device to provide power t ...

. This will usually be a visual indication of the battery's

state of charge State of charge (SoC) is the level of charge of an electric battery relative to its capacity. The units of SoC are percentage points (0% = empty; 100% = full). An alternative form of the same measure is the depth of discharge (DoD), the inverse ...

. It is particularly important in the case of a

battery electric vehicle A battery electric vehicle (BEV), pure electric vehicle, only-electric vehicle, fully electric vehicle or all-electric vehicle is a type of electric vehicle (EV) that exclusively uses chemical energy stored in rechargeable battery packs, wi ...

Automobiles

Some

automobile A car or automobile is a motor vehicle with wheels. Most definitions of ''cars'' say that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people instead of goods. The year 1886 is regarded ...

s are fitted with a battery condition meter to monitor the

starter battery An automotive battery or car battery is a rechargeable battery that is used to start a motor vehicle. Its main purpose is to provide an electric current to the electric-powered starting motor, which in turn starts the chemically-powered internal ...

. This meter is, essentially, a

voltmeter A voltmeter is an instrument used for measuring electric potential difference between two points in an electric circuit. It is connected in parallel. It usually has a high resistance so that it takes negligible current from the circuit. An ...

but it may also be marked with coloured zones for easy visualization. Many newer cars no longer offer voltmeters or ammeters; instead, these vehicles typically have a light with the outline of an automotive battery on it. This can be somewhat misleading as it may be confused for an indicator of a bad battery when in reality it indicates a problem with the vehicle's charging system. Alternatively, an

ammeter An ammeter (abbreviation of ''Ampere meter'') is an instrument used to measure the current in a circuit. Electric currents are measured in amperes (A), hence the name. For direct measurement, the ammeter is connected in series with the circuit ...

may be fitted. This indicates whether the battery is being charged or discharged. In the adjacent picture, the ammeter is marked "Alternator" and the symbols are "C" (charge) and "D" (discharge). Both

s and

s individually or together can be used to assess the operating state of an automobile battery and charging system.

Electronic devices

A battery indicator is a feature of many electronic devices. In

mobile phone A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive telephone call, calls over a radio freq ...

s, the battery indicator usually takes the form of a

bar graph A bar chart or bar graph is a chart or graph that presents categorical data with rectangular bars with heights or lengths proportional to the values that they represent. The bars can be plotted vertically or horizontally. A vertical bar chart is ...

- the more bars that are showing, the better the battery's state of charge.

Computers

Computers may give a signal to users that an internal standby battery needs replacement. Portable computers using rechargeable batteries generally give the user some indication of the remaining operating time left on the battery. A Smart Battery System uses a controller integrated with an interchangeable battery pack to provide a more accurate indication of the state of battery charge.

Batteries not part of a system

Batteries that are part of a system, such as computer batteries, can have their properties checked and logged in operation to assist in determining remaining charge. A real battery can be modeled as an ideal battery with a specified EMF, in series with an

internal resistance A practical electrical power source which is a linear electric circuit may, according to Thévenin's theorem, be represented as an ideal voltage source in series with an impedance. This impedance is termed the internal resistance of the source. ...

. As a battery discharges, the EMF may drop or the internal resistance increase; in many cases the EMF remains more or less constant during most of the discharge, with the voltage drop across the internal resistance determining the voltage supplied. Determining the charge remaining in many battery types not connected to a system that monitors battery use is not reliably possible with a voltmeter. In battery types where EMF remains approximately constant during discharge, but resistance increases, voltage across battery terminals is not a good indicator of capacity. A meter such as an equivalent series resistance meter (

ESR meter An ESR meter is a two-terminal electronic measuring instrument designed and used primarily to measure the equivalent series resistance (ESR) of real capacitors; usually without the need to disconnect the capacitor from the circuit it is conne ...

) normally used for measuring the ESR of electrolytic capacitors can be used to evaluate internal resistance.Use of ESR meter to measure battery resistance, indicator of state of charge
/ref> ESR meters fitted with protective diodes cannot be used, a battery will simply destroy the diodes and damage itself. An ESR meter known not to have diode protection will give a reading of internal resistance for a rechargeable or non-rechargeable battery of any size down to the smallest

button cell A button cell, watch battery, or coin battery is a small single-cell battery shaped as a squat cylinder typically in diameter and high — resembling a button. Stainless steel usually forms the bottom body and positive terminal of the cell; i ...

s which gives an indication of the state of charge. To use it, measurements on fully charged and fully discharged batteries of the same type can be used to determine resistances associated with those states. The cost of an ESR meter makes it uneconomic for measuring battery voltages as its only function, but a meter used for cheeking capacitors can take on the additional duty.

References

Battery (electricity) Measuring instruments Auto parts

Automobiles

Electronic devices

Computers

Batteries not part of a system

See also

References