GLOSSARY
Car Battery Terms Explained: A Plain-English Glossary
Written by the 800Battery team ·
QUICK ANSWER
The numbers on a car battery label describe three things: how much energy it stores (Ah), how much current it can deliver to start the engine (CCA), and its physical size and terminal layout (a DIN or JIS code). The technology, such as AGM or EFB, tells you which cars it suits. This glossary defines each term in plain language.
Key facts
- Ah (amp-hours): how much energy the battery stores
- CCA (cold cranking amps): how much starting current it can deliver
- DIN and JIS: the European and Japanese size standards
- AGM and EFB: the two technologies made for start-stop cars
- All standard car batteries are 12V
Numbers on the label
| Term | What it means |
|---|---|
| Voltage (V) | Electrical pressure. Car batteries are nominally 12V; a fully charged one rests at about 12.6V or a little higher. |
| Capacity (Ah, amp-hours) | How much energy the battery stores. A 70Ah battery can in principle supply 3.5 amps for 20 hours. Larger cars and cars with more electronics need more. |
| CCA (cold cranking amps) | The current a battery can deliver for 30 seconds at -18°C while staying above a minimum voltage. It is the standard measure of starting power, and useful in hot countries too, because it falls as the battery ages. |
| RC (reserve capacity) | How many minutes a full battery can supply 25 amps before it is flat. It indicates how long the car's electrics would run if the alternator failed. |
| Date code | A stamped or printed code showing when the battery was made. Formats differ between manufacturers, so ask the fitter to read it for you. |
Battery technologies
| Term | What it means |
|---|---|
| Lead-acid | The chemistry of almost every 12V car battery: lead plates in sulphuric acid electrolyte. Standard, calcium, EFB, AGM and Gel are all lead-acid types. |
| Flooded (wet cell) | A battery with free liquid electrolyte. The conventional design. |
| Calcium | A flooded battery with calcium-alloy grids, which lose less water and self-discharge more slowly. Most maintenance-free batteries are this type. |
| EFB (Enhanced Flooded Battery) | A reinforced flooded battery that tolerates more charge cycles. Made for entry-level start-stop cars. |
| AGM (Absorbent Glass Mat) | A sealed battery with the electrolyte held in glass-fibre mats. Made for advanced start-stop systems and heavy electrical loads. |
| Gel | A sealed battery with the electrolyte set as a gel. Good at deep cycling; used mainly for auxiliary and leisure applications. |
| Lithium-ion (12V) | A lighter battery with a built-in management system, fitted from the factory on some performance, hybrid and electric cars. |
| Maintenance-free | A sealed design that never needs topping up with water. |
| VRLA | Valve-regulated lead-acid. The family name for sealed AGM and Gel batteries. |
Which type your car needs is covered in AGM vs EFB vs lead-acid.
Sizes and fitment
| Term | What it means |
|---|---|
| DIN / EN size | The European size standard. Batteries share a common width and vary in length, with recessed terminals. Used on European cars. |
| JIS size | The Japanese Industrial Standard. A code such as 55D23L gives a performance rank, the case size, the length in centimetres and which side the terminal is on. Used on Japanese and Korean cars. |
| BCI group size | The North American size standard, used on American cars. |
| Terminal layout | Which side the positive post is on. The wrong layout means the cables will not reach. |
| Hold-down | The clamp or bracket that secures the battery. A loose battery is damaged by vibration. |
Systems in the car
| Term | What it means |
|---|---|
| Alternator | The engine-driven generator that powers the car's electrics and recharges the battery while you drive. |
| Start-stop | A system that switches the engine off when the car is stationary and restarts it when you move off. It needs an EFB or AGM battery. |
| BMS (battery management system) | Electronics that monitor the battery and control how it is charged. |
| IBS (intelligent battery sensor) | The sensor, usually on the negative terminal, that feeds the BMS. |
| Battery registration | Telling the car that a new battery has been fitted so it resets its charging strategy. Required on many modern cars. |
| Battery coding | Changing the car's settings when the new battery differs in type or capacity from the old one. |
| Auxiliary battery | A second, smaller battery that supports start-stop or other systems on some cars, notably many Mercedes models. |
| Memory keeper | A device that keeps the car's electronics powered during a battery swap so settings are not lost. |
Registration and coding are part of our AGM and start-stop battery service.
Faults and failure
| Term | What it means |
|---|---|
| State of charge (SoC) | How full the battery is right now, as a percentage. |
| State of health (SoH) | How much of its original performance the battery has left. A battery can be fully charged and in poor health. |
| Sulphation | Lead sulphate crystals hardening on the plates when a battery is left discharged. It permanently reduces capacity. |
| Grid corrosion | The gradual breakdown of the lead grids. It speeds up with heat and is the main way batteries wear out in hot climates. |
| Parasitic drain | Current drawn while the car is parked and switched off. A small amount is normal; a fault can flatten a battery overnight. |
| Deep discharge | Running a battery nearly flat. Starter batteries are not designed for it and are damaged by repeated deep discharges. |
| Jump start (boost) | Starting a car with a flat battery using an external power source. |
| Conductance test | A quick electronic test that estimates a battery's health against its rated CCA. |
See how these are measured in our free battery test, and how heat drives corrosion in the battery life guide.
FREQUENTLY ASKED QUESTIONS
What does CCA mean on a car battery?
Cold cranking amps: the current the battery can deliver for 30 seconds at -18°C while holding a minimum voltage. It measures starting power. Fit a battery with at least the CCA your car was specified with.
What does Ah mean on a battery?
Amp-hours, a measure of how much energy the battery stores. Fit at least the capacity the car was built with.
Is CCA important in a hot country like the UAE?
Yes. The engine needs less current to start in warm weather, but CCA is still the standard way to rate a battery, and a falling measured CCA is how a tester detects that a battery is wearing out.
What is the difference between DIN and JIS batteries?
They are different size standards. DIN is European, with recessed terminals and a common width. JIS is Japanese, with its own case sizes and codes. The two are not generally interchangeable in the same tray.
What is battery registration?
On cars with a battery management system, registration tells the car a new battery has been fitted so it charges it correctly. Skipping it can shorten the new battery's life.
KEEP READING
