There are several different terms used in the battery context, and in this article, you will find an explanation of the most common terms.

AGM, absorbing glass matt

A type of lead-acid battery that you can read more about in the article Electrical system, part 3 – Facts about lead batteries.

Ah, Ampere hours

A measure of the battery’s total capacity, the same as energy content.

Anode

The negative terminal of a battery.

BMS, battery management system

A device that controls charging so that the battery cells in a battery maintain the same voltage. There are also BMS that regulate the voltage of the batteries in a battery bank.

C-rate

Specifies the current that discharges the battery completely in a certain time.

• 10C corresponds to a current that drains the battery in 1/10 hour (6 minutes).
• C or 1C corresponds to a current that drains the battery in 1 hour.
• C/10 corresponds to a current that drains the battery in 10 hours.
  Sometimes it is written 0.1C or C₁₀
• C/20 corresponds to a current that drains the battery in 20 hours.
  Sometimes it is written as 0.05C or C₅
  The energy drained at this current is often used to specify the nominal capacity (energy content) of the battery in Ah. A battery containing 100Ah will be completely discharged in 20 hours when the current is 5A (5A x 20h = 100 Ah).

CA, cranking amps

Same as CCA but at 0 degrees Celsius.

Capacity

Indicates how much energy the battery contains, which can be specified as Ah or Wh. The amount of energy that can be extracted from a fully charged battery depends on the battery’s condition, temperature, and how strong current that is extracted. Usually, the capacity is measured at 20 degrees Celcius and with a consumption current of C/20 (0.05C), i.e. the battery is fully discharged in 20 hours.

The capacity decreases the higher current is taken out. The capacity also decreases at lower temperatures.

Conversion between Wh and Ah is done with the formula below.

Wh = Ah x Nominal voltage.

Cathode

The positive terminal of a battery.

CCA, cold cranking amps

The current the battery can deliver at a temperature of -18 degrees Celsius for 30 seconds and the battery voltage drops to 7.5V for a battery with a nominal voltage of 12V. The measurement is most relevant for starter batteries.

Charging cycle

The process when a battery is charged from its lowest recommended SoC until fully charged is called a charge cycle.

Charging step

Indicates the different methods a charger uses when charging a battery.

Corrosion of battery terminals lead-acid battery

See Electrical system, Part 3 – Facts about lead batteries

Circular battery terminals

The battery cell consists of two large plates that have been rolled together. The advantage is that they are said to emit a greater effect than flat plates do.

Deep cycle

Indicates that a battery can withstand being discharged more than is usual for the battery type. Most often used to describe the properties of a lead-acid battery, which is built with thicker plates in the battery terminals. This allows the battery to withstand more deep discharges and more charge cycles.

DoD, depth of discharge

Indicates how much the battery has been discharged.
0% means the battery is fully charged. 100% means that the battery is completely discharged. This metric is the opposite of SoC.

EFB, enhanced flooded battery

Like a flooded battery where the plates of the positive pole have been covered with a plastic fabric. Has approximately twice as many charge cycles as a conventional starter battery.

Efficiency

How much of the supplied energy is returned when using the battery. When charging, part of the added energy is lost as heat, the same thing when discharging.

The greater the charging/discharging current is, the greater the losses.

Since batteries are affected by the temperature around them, efficiency will also be affected by the ambient temperature. In principle, the efficiency decreases with increasing temperature within the battery’s temperature range.

Sometimes the term is used to indicate efficiency during charging, i.e. how much of the added energy is stored in the battery.

Sometimes the term is used to indicate efficiency during discharge, i.e. how much of the stored energy is released as electric current.

A battery also has self-discharge, which also affects efficiency, but that loss is usually not taken into account when speaking of the efficiency of a battery.

Equipment used to protect the battery bank does also use electricity from the battery, affecting the efficiency of the battery bank. Ex. on such equipment are Undervoltage protection and BMS which are often used for LFP batteries.

Energy density

How much energy the battery can store per kg, is measured in Wh/kg.

Since different types of batteries can be discharged to different levels of DoD without being damaged, it is more relevant to know the practical energy density. It is the energy density calculated on the energy that can be taken out of the battery at the DoD that does not damage the battery.

Flooded

Indicates that the electrolyte in a lead-acid battery is liquid.

GEL (GELled electrolyte)

A type of lead-acid battery.

Internal resistance

All batteries have internal resistance and lead-acid batteries have a higher resistance than Lithium-ion batteries. The internal resistance increases with increasing SoC, this is what causes the charging current to decrease the more charged the battery is. Ohm’s law U=R*I means that at constant voltage, I decreases as R increases.

kW (kilo Watt)

Unit for 1000W. See also the concept of W further down the list.

Lead-Carbon battery

The negative terminal of a lead-acid battery has a structure made of carbon.

Lead-Calcium battery

The battery terminals in a lead-acid battery have a grid made of calcium alloy.

Leisure battery

I’m not sure this term is used in the English vocabulary, maybe Service battery is better.

Marine battery

I’m not sure this term is used in the English vocabulary, maybe Service battery is better.

Open battery

A lead-acid battery with battery cells where more electrolyte can be added.

Power

Tells how much maximum current a battery can deliver without the voltage dropping too much. CCA is such a measure.

Peukert’s lag

It is a formula that indicates how quickly the charge in a battery drops at a certain current draw. The greater the current, the less energy you can extract from the battery before it is discharged.

The formula looks like this

t = H(C/IH)^k

The formula contains a parameter (k) that can have a value between 1 and 1.5. It is typical for the type of battery. The value of the parameter for a particular type of battery is called Peukert’s constant for that battery.

The other parameters in the formula are t which indicates how many hours the battery will last when it leaves the current I. C indicates the capacity of the battery in Ah and H indicates the current used when C was measured.

The formula does not take into account the temperature or age of the battery. In general, Peukert’s constant increases with increasing temperature. It also increases with the increasing age of the battery.

A higher value of Peukert’s constant means that there is less available energy in the battery.

The formula primarily applies only to lead-acid batteries. LFP batteries basically have Peukert’s constant = 1.

Prismatic battery cell

The battery cell consists of one or more rectangular plates.

Service battery

Indicates that the battery is built to withstand greater discharge than a starter battery and also withstand more charge cycles.

Sealed battery

Indicates that a lead-acid battery has closed battery cells and it is therefore not possible to top up with electrolyte.

Shedding

See Electrical system, part 3 – Facts about lead-acid batteries

SLI battery (Start Lighting Ignition)

Term for a battery suitable as a starter and consumption battery (mostly in cars).

SMF, sealed maintenance free

Another term for VRLA.

SoC (State of Charge)

Indicates how much the battery is charged. 100% means the battery is fully charged. 0% means that the battery is completely discharged. This measure is reversed compared to DoD.

Starter battery

Indicates that the battery is intended to be used as a starter battery, i.e. it can emit a large current (has a large effect) in relation to its capacity. However, it cannot withstand being discharged that much, should preferably not be discharged (DoD) more than 30% (SoC = 70%). A starter battery has more and thinner plates in the battery poles compared to a service battery. This allows them to deliver more current but handle fewer charge cycles.

Stationary battery

Is a battery that is intended to be used as backup power and most of the time it is fully charged. Not so suitable for use as a service battery.

Stratification

See Electrical system, part 3 – Facts lead-acid batteries

Sulfatering

See Electrical system, part 3 – Facts lead-acid batteries

Traction-battery

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Indicates that the battery is intended to be used in work vehicles and withstand deep discharge and high current draw and can be recharged many times. They have roughly the same properties as a deep-cycle battery.

Unvented battery

The battery is gas-tight and equipped with a safety valve to be able to release an excess of hydrogen gas. Same thing as a sealed battery.

Ventilated battery

Indicates that the battery emits hydrogen and other gases formed in the battery cells. Same thing as a sealed battery or a VRLA battery.

VRLA (Valve Regulated Lead-Acid)

Named because there is a safety valve on the closed lead-acid battery that allows it to release an excess of gases from the battery.

W (Watt)

Unit of power and is used to indicate how strong the lamp, the motor, or other equipment is.

Wh (Watt Hours)

Unit of energy and is used to indicate the battery capacity.

Suppose a 12V battery and a 24V battery are rated 100Ah. Since the voltage is twice as high in the 24V battery, the capacity is also twice as great in the 24V battery.

The capacity of the 12V battery is 12V * 100Ah = 1200 Wh.

The capacity of the 24V battery is 24V * 100Ah = 2400 Wh.