Written by the Silicon Oasis Car Battery team ·
Key points
- Replace AGM with AGM. Replace EFB with EFB or AGM. Replace standard with standard, or upgrade if it suits the car.
- The label on the battery fitted now tells you which type the car uses.
- AGM and EFB cost more because they survive far more charge cycles.
- Many European cars need a new battery registered with the car's computer.
The three types side by side
| Standard flooded | EFB | AGM | |
|---|---|---|---|
| Full name | Flooded lead-acid, also called SLI or wet cell | Enhanced flooded battery | Absorbent glass mat |
| Construction | Lead plates in liquid acid | Flooded, with reinforced plates and a fabric layer that holds the active material in place | Acid absorbed in glass-fibre mats pressed between the plates, in a sealed case |
| Charge cycles | Baseline | Roughly twice a standard battery | Roughly three times a standard battery |
| Start-stop | Not suitable | Yes, basic systems | Yes, including brake-energy recovery |
| Deep discharge | Tolerates it poorly | Tolerates it better | Recovers best |
| Spill-proof | No | No | Yes |
| Relative price | Lowest | Middle | Highest |
| Typical cars | Older and simpler cars without start-stop | Compact and mid-size start-stop cars | European premium cars, large SUVs with start-stop, cars with many electrical consumers |
All three are 12V lead-acid batteries and look alike from the outside. The differences are inside, in how they cope with being drained and recharged again and again.
How to tell which battery your car has
- Read the label. AGM and EFB batteries say so, often with the words Start-Stop.
- Look for a start-stop button on the dashboard, usually an A inside a circular arrow.
- Look at the negative terminal. A small electronic sensor clamped to it means the car monitors its battery and probably needs registration.
- Check the handbook, or send us the make, model and year and we look it up.
Can you downgrade or upgrade?
Downgrading is the mistake to avoid. A standard battery in a start-stop car is cycled far harder than it was designed for. It usually fails early, and the car often disables start-stop long before that.
Upgrading is possible: EFB can replace standard, and AGM can replace either. It makes sense for cars that make many short trips or carry extra electrical equipment. It is not automatically better, because the car's charging system is set up for the original type. On cars with battery management, the new type must be coded in.
Battery registration and coding
Cars with a battery management system track the battery's age and adjust charging as it wears. When a new battery goes in, the car has to be told. Registration resets that record. Coding goes a step further and tells the car that the capacity or type has changed.
Skipping this step means a new battery is charged as if it were the old one. The usual results are a shorter battery life, warning messages and start-stop that stays switched off. Many BMW, Mini, Audi, Volkswagen, Mercedes-Benz, Land Rover and Ford models need it. Most Japanese and Korean cars without a battery sensor do not.
Which type copes best with UAE heat?
Heat ages every lead-acid battery. AGM and EFB handle the stop-start cycling and partial charge of city driving better than a standard battery, which is where much of their advantage comes from. AGM copes poorly with high heat and with overcharging. Heat is one reason many manufacturers mount it in the boot, away from the engine, and overcharging is why correct registration matters.