Car battery glossary

AGM

AGM stands for Absorbent Glass Mat, a sealed battery in which the acid is soaked into glass-fibre mats between the plates. It cannot spill, handles deep cycling and is fitted to cars with advanced start-stop and heavy electrical loads.

Alternator

An alternator is the engine-driven generator that recharges the battery and powers the car's electrics while the engine runs. If it fails, the battery warning light comes on and the car runs on the battery alone until it stops.

Ampere-hour (Ah)

Ampere-hour, written Ah, is the unit of battery capacity. It tells you how much electrical energy the battery stores: a 70 Ah battery can in theory supply 3.5 amps for 20 hours before it is empty.

Auxiliary battery

An auxiliary battery is a small second battery fitted to many Mercedes models and some other cars. It keeps the electronics stable during start-stop restarts, and a dashboard message appears when it weakens.

Battery management system (BMS)

A battery management system, or BMS, is the sensor and control software that track the 12V battery's charge, temperature and age. It adjusts alternator charging to suit and decides when start-stop is allowed to work.

Battery registration

Battery registration is the scan-tool step that tells the car a new battery has been fitted. It clears the stored ageing data so the charging system treats the battery as new and not as the worn one it replaced.

Battery sensor (IBS)

A battery sensor, called IBS on BMW, is a small electronic unit clamped to the negative terminal. It measures current, voltage and temperature and reports them to the car so that charging can be controlled precisely.

CCA

CCA stands for cold cranking amps, the current a battery can deliver in a short burst at minus 18 C. It indicates starting power, and a replacement battery should meet or exceed the figure the car maker specifies.

Conductance test

A conductance test is the quick electronic check a technician runs with a handheld tester. It sends a small signal through the battery to judge the condition of the plates without discharging it, then prints a pass or replace result.

Deep discharge

Deep discharge means a battery has been drained far below its normal working level, for example by lights left on overnight. Starter batteries are not built for it, and each episode permanently removes some capacity.

DIN size

DIN size refers to the European standard for battery cases, with recessed terminals and a fixing lip along the base. European cars and many newer American ones use DIN sizes, which are identified by case length and height.

EFB

EFB stands for Enhanced Flooded Battery, a strengthened version of the conventional battery with about twice the cycle life. It is fitted to cars with basic start-stop and can be replaced by EFB or upgraded to AGM.

Electrolyte

Electrolyte is the mixture of sulphuric acid and water inside a lead-acid battery that lets current flow between the plates. Heat evaporates the water over time, which is one reason batteries age quickly in the Gulf.

Flooded battery

A flooded battery is the conventional type in which the plates sit in liquid electrolyte. Modern versions are sealed and maintenance-free, and they suit most cars that do not have start-stop.

Grid corrosion

Grid corrosion is the slow eating away of the lead frames that hold the active material in each plate. High temperature speeds it up sharply, and it is the main reason car batteries wear out in hot countries.

JIS size

JIS size refers to the Japanese standard for battery cases, used on most Japanese and many Korean cars. The cases are taller with raised terminals, and a code such as 55D23L describes performance, dimensions and terminal position.

Jump start

A jump start is a way of starting a car with a flat battery by lending it power from a jump pack or another vehicle. It gets the engine running but does not repair a battery that has worn out.

Maintenance-free battery

A maintenance-free battery is a sealed design that never needs topping up with water during its life. Calcium alloy grids keep water loss low, and nearly all car batteries sold in the UAE today are of this kind.

Memory saver

A memory saver is a small power supply plugged into the car while the battery is changed. It keeps the control units alive so the clock, radio presets, window settings and learned values are not lost.

Parasitic drain

Parasitic drain is the current a car keeps drawing after it is switched off and locked. A small amount is normal for alarms and computers, but a faulty module or accessory can flatten a healthy battery in days.

Reserve capacity

Reserve capacity is the number of minutes a fully charged battery can supply a steady 25 amps before its voltage drops too low. It shows how long the car could run its essentials if the alternator stopped charging.

Resting voltage

Resting voltage is the reading across the terminals after the car has been switched off for a few hours. Around 12.6 volts or more means fully charged, while 12.2 volts is roughly half and calls for charging.

Smart alternator

A smart alternator is one whose output is controlled by the engine computer and does not stay constant. It charges hardest while the car is slowing down to save fuel, which is why these cars need EFB or AGM batteries.

Start-stop

Start-stop is the fuel-saving system that switches the engine off when the car is stationary and restarts it when you release the brake. It multiplies the number of starts, so it needs an EFB or AGM battery.

State of charge

State of charge, shortened to SoC, is how full a battery is at this moment, given as a percentage. A low reading can be fixed by driving or charging and says nothing on its own about the battery's condition.

State of health

State of health, shortened to SoH, compares what a battery can deliver now with what it could deliver when new. Unlike state of charge it cannot be restored, and a low figure means replacement is due.

Sulphation

Sulphation is the build-up of hard lead sulphate crystals on the plates of a battery that has been left discharged. The crystals block the chemical reaction, so the battery loses capacity and may no longer accept a full charge.

Terminal

A terminal is one of the two lead posts, positive and negative, where the car's cables clamp onto the battery. Loose or corroded terminals cause starting trouble that is easily mistaken for a failed battery.

Vent tube

A vent tube is the thin hose that carries charging gases from the battery to the outside of the car. It matters most when the battery sits in the boot or cabin, and it must be reconnected after a replacement.

Warranty

Warranty is the maker's cover against manufacturing defects in a battery, confirmed by a test. On the batteries we fit it runs up to 24 months depending on brand and type, and it excludes damage and misuse.

An AGM car must get AGM back. An EFB car can take EFB or step up to AGM. A standard battery in a start-stop car will fail early and switch the start-stop off.

More guides

• How Long Does a Car Battery Last in UAE Heat? Sharjah Guide
• Jump Start or New Battery? How to Decide in Sharjah, UAE
• Battery, Alternator or Starter: Which One Failed? UAE Guide
• AGM vs EFB vs Flooded Battery: What Your Car Needs in the UAE
• How to Jump Start a Car Safely: Step-by-Step Guide for UAE
• Battery Registration and Coding Explained for UAE Drivers
• Dead Battery in Basement Parking: What to Do in Al Taawun
• Which Car Battery Brand to Choose in the UAE: An Honest Guide
• Car Battery Warranty Explained: What Is and Is Not Covered
• What Decides the Cost of a Car Battery in Sharjah and the UAE