Car Battery Glossary: Terms Explained in Plain Words
The three terms that matter most when buying a battery are Ah (amp-hours — how much energy it stores), CCA (cold cranking amps — how much starting power it delivers) and the technology (standard flooded, EFB or AGM). The rest of this glossary covers the words you will hear from a technician or read on a battery label.
- Ah
- Stored energy
- CCA
- Starting power
- AGM / EFB
- Start-stop types
- Load test
- Real health check
Last reviewed 2 October 2026
Ratings on the battery label
| Term | Meaning |
|---|---|
| Ah (amp-hour) | Capacity: how much energy the battery stores. Car battery capacity is usually given at a 20-hour discharge rate. Bigger engines and more electronics need more Ah. |
| CCA (cold cranking amps) | Starting power: the current a 12-volt battery can deliver for 30 seconds at −18°C while staying at or above 7.2 volts. Higher is stronger. |
| RC (reserve capacity) | How many minutes the battery can run the car's essentials if the charging system fails. |
| Voltage | Car batteries are nominally 12 volts. A healthy, rested battery reads about 12.6 volts or more. |
| Date code | A stamp or sticker showing when the battery was made. Fresher stock is better. |
Battery types
| Term | Meaning |
|---|---|
| Lead-acid battery | The standard car battery chemistry: lead plates in sulphuric acid electrolyte. |
| Flooded / standard / SLI | A conventional battery with free liquid electrolyte, built for starting, lighting and ignition on cars without start-stop. |
| Maintenance-free | A sealed design that does not need topping up with water during its life. |
| EFB (Enhanced Flooded Battery) | A strengthened flooded battery for entry-level start-stop cars, with a higher cycle life than a standard one. |
| AGM (Absorbent Glass Mat) | A sealed battery with electrolyte absorbed in glass-fibre mats. The strongest type for start-stop and heavy electrical loads. See AGM and start-stop batteries. |
| 12 V auxiliary battery | The small 12-volt battery in a hybrid or electric car that powers the electronics and wakes the high-voltage system. It can go flat like any other. |
Sizes and fitment
| Term | Meaning |
|---|---|
| JIS | The Japanese sizing standard, used on most Japanese and Korean cars. A code such as 55D23L encodes performance, case size, length and terminal side. |
| DIN / EN | The European sizing standard, used on European cars. Sizes are often written as L2, L3 or H5, H6 and so on. |
| BCI group | The North American sizing standard, used on many American cars. |
| Terminal layout (polarity) | Which side the positive and negative posts sit on. It must match the car or the cables will not reach. |
| Hold-down | The clamp or lip that fixes the battery in its tray. A loose battery is damaged by vibration. |
Testing and health
| Term | Meaning |
|---|---|
| Load test | A test of how the battery performs when asked for starting current. The reliable way to judge a battery. See battery testing. |
| State of charge (SoC) | How full the battery is right now. |
| State of health (SoH) | How much of its original capacity the battery still has. A worn battery can be fully charged and still fail. |
| Alternator | The engine-driven generator that recharges the battery and powers the car while the engine runs. |
| Charging voltage | The voltage at the battery with the engine running, typically around 13.7 to 14.7 volts. |
| Parasitic drain | The small current a parked car draws for its alarm, tracker and control units. Too much of it flattens the battery. |
| Self-discharge | The charge a battery loses on its own while sitting. It speeds up in heat. |
| Sulfation | Hard lead-sulphate crystals that form when a battery sits discharged, permanently reducing capacity. |
| Deep discharge | Draining a battery nearly flat. Standard starter batteries are damaged by it. |
Service terms
| Term | Meaning |
|---|---|
| Jump start (boost) | Starting a car with a flat battery from an external power source. See jump start service. |
| Start-stop | A system that switches the engine off when the car is stationary and restarts it automatically. |
| Battery registration / coding | Telling the car's computer that a new battery has been fitted, so it charges it correctly. Required on many European cars. |
| IBS (Intelligent Battery Sensor) | A sensor on the negative terminal that measures current, voltage and temperature for the car's energy management. |
| BMS (Battery Management System) | The software that monitors the battery and controls charging. |
| Memory saver | A device that keeps the car's electronics powered during a battery swap, so radio, clock and seat settings are kept. |
| Battery maintainer | A low-current smart charger that keeps a parked car's battery topped up. |
| OEM / OE | Original equipment: the brand or specification the car maker fitted at the factory. |
Common questions
Ah (amp-hours) is capacity — how much energy the battery stores. CCA (cold cranking amps) is starting power — how much current it can deliver to turn the engine. A replacement should meet or exceed the manufacturer's figures for both.
Both are built for start-stop cars. EFB is a strengthened flooded battery for entry-level systems. AGM is sealed, with the electrolyte held in glass mat, and handles more cycles and heavier electrical loads.
The size is set by the car's battery tray and terminal positions, and is written as a JIS, DIN or BCI code on the old battery's label. Send us a photo of the label, or the make, model and year, and we match it.
It is the step of telling the car's computer that a new battery has been fitted, so the charging system treats it as new. Many BMW, MINI, Audi, Volkswagen and Land Rover models need it.
Keep reading
Dead battery? We come to where the car is parked.
Call or send your community and villa number on WhatsApp — no forms, no waiting on hold.