Car battery glossary
Plain-language definitions of the terms on a battery label and on your invoice.
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Battery glossary
The words mechanics use about batteries, explained in a sentence or two each. Linked from our guides whenever a term needs it.
- AGM (Absorbent Glass Mat)
- A sealed lead-acid battery in which the acid is absorbed in glass-fibre mats pressed between the plates. It handles frequent charge cycles and vibration well, and is fitted to cars with advanced start-stop or heavy electrical loads.
- Ah (amp-hours)
- A measure of how much energy a battery stores. A 70 Ah battery can in theory supply 3.5 amps for 20 hours, the standard test period. Higher Ah means longer support for electrical loads with the engine off.
- Alternator
- The belt-driven generator that powers the car's electrics and recharges the battery while the engine runs. A healthy system typically shows about 13.5 to 14.8 V at the battery terminals with the engine running.
- Auxiliary battery
- A second, usually smaller 12 V battery fitted to some cars to support start-stop restarts or electronic systems alongside the main battery. In hybrid and electric cars the 12 V battery is itself often called the auxiliary battery.
- Battery registration (BMS coding)
- Telling the car's battery management system, through a diagnostic tool, that a new battery has been fitted, along with its type and capacity. The car then resets its charging strategy. Many European models and other cars with battery sensors require it.
- Battery terminal
- One of the two lead posts on a battery, positive (+) and negative (-), where the car's cable clamps attach. Loose or corroded terminals cause poor starting and poor charging even when the battery itself is healthy.
- Booster pack
- A portable battery unit with its own clamps that supplies the current needed to start a car with a flat battery, without a second vehicle. Technicians carry professional units sized for large petrol and diesel engines.
- Calcium battery
- A lead-acid battery whose grids are made from a lead-calcium alloy in place of the older lead-antimony type. It loses less water and self-discharges more slowly, which is why most modern sealed car batteries are calcium batteries.
- CCA (cold cranking amps)
- A rating of starting power. Under the SAE method it is the current a fully charged 12 V battery can deliver for 30 seconds at minus 18°C while staying above 7.2 V. A replacement battery must meet the car maker's figure.
- Conductance test
- A quick electronic test in which a handheld tester passes a small signal through the battery and measures how well it conducts. The result estimates the remaining starting current and health without discharging the battery.
- Date code
- A sticker or stamp on the battery showing when it was made or dispatched. Formats vary by manufacturer. Some show the month and year in numbers, others use a letter for the month and a digit for the year.
- Deep discharge
- Draining a battery far below its normal working range, typically under about 12.0 V at rest or until the car will not start. Each deep discharge permanently removes some capacity from a starter battery, especially in hot weather.
- DIN, JIS and BCI size standards
- Three systems that define a battery's case dimensions, terminal type and layout. DIN and the related EN sizes are European, JIS is Japanese and BCI group sizes are North American. A replacement must match the car's tray and cables.
- EFB (Enhanced Flooded Battery)
- A liquid-acid battery strengthened with thicker plates, a polyester scrim on the positive plates and carbon additives. It lasts through roughly twice as many charge cycles as a standard flooded battery and suits basic start-stop cars.
- Flooded battery
- The conventional car battery, with lead plates immersed in liquid sulphuric acid. It is designed to give a short, strong burst of starting current and is used in cars without start-stop. Also called a wet battery.
- Grid corrosion
- The gradual breakdown of the lead grids that support the plates and carry current, mainly on the positive side. Heat speeds it up sharply, and it is the main reason car batteries wear out sooner in Gulf climates.
- IBS (intelligent battery sensor)
- A small electronic sensor fixed to the battery's negative terminal. It measures current, voltage and temperature and reports them to the battery management system, which uses the data to control charging and start-stop.
- Jump start
- Starting a car that has a flat battery by connecting it with cables to another vehicle's battery or to a booster pack. It gets the engine running but does not repair or fully recharge the battery.
- Load test
- A test that draws a heavy current from the battery for several seconds, typically about half its CCA rating for 15 seconds, while watching the voltage. A healthy 12 V battery stays above roughly 9.6 V.
- Maintenance-free battery
- A sealed battery that never needs topping up with distilled water during its service life. Most modern car batteries are of this kind. The name refers only to water, and the battery still needs testing and clean, tight terminals.
- Memory saver
- A small power supply connected through the diagnostic port or a 12 V socket while the battery is changed. It keeps the car's stored settings alive, such as the clock, radio presets, seat memory and window positions.
- Parasitic drain
- Current drawn from the battery while the car is switched off and locked. A small draw for the alarm, clock and control units is normal. A faulty module, a light left on or an added accessory can raise it and flatten the battery within days.
- Reserve capacity (RC)
- The number of minutes a fully charged battery can supply 25 amps at about 27°C before its voltage falls to 10.5 V. It indicates how long the car's essential electrics could run if the alternator stopped charging.
- Start-stop system
- A fuel-saving system that switches the engine off when the car stops, at a traffic light for example, and restarts it when the driver releases the brake. It needs an EFB or AGM battery and stops working when the battery is weak.
- State of charge (SoC)
- How full a battery is at a given moment, shown as a percentage. A rested 12 V battery reads about 12.6 V or more when full, about 12.4 V at 75% and about 12.2 V at 50%.
- State of health (SoH)
- How much of its original performance an ageing battery still has, compared with when it was new. A tester estimates it from the measured starting current against the rated figure. A battery can be fully charged and still be in poor health.
- Sulphation
- The build-up of hard lead sulphate crystals on the plates of a battery that is left partly or fully discharged. The crystals block the active material, so the battery holds less charge and accepts charge more slowly.
- Trickle charger
- A low-current mains charger that keeps a parked car's battery topped up over days or weeks. Smart versions, often called maintainers, switch on and off automatically so the battery is not overcharged.
Battery guides
- How Long Do Car Batteries Last in Dubai?
- Signs Your Car Battery Is About to Fail
- AGM vs EFB vs Flooded Car Batteries: Which Do You Need?
- How to Jump Start a Car Safely: Step-by-Step Guide
- Car Won't Start: Is It the Battery, Alternator or Starter?
- What Decides the Cost of a Car Battery Replacement in Dubai
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