Know what you're buying
Start-Stop, AGM, EFB: which battery does your car actually need?
If your car switches the engine off at red lights, its battery works several times harder than a classic one — and replacing it is not a like-for-like commodity purchase. Here's what the acronyms mean, in plain English, and what a correct replacement involves.
Three technologies, one rule
Flooded (standard). The classic lead-acid battery. Fine for cars without Start-Stop: one start per journey, steady charging, predictable life.
EFB — Enhanced Flooded Battery. A reinforced flooded design for entry-level Start-Stop systems: thicker plates, better cycling. Fitted to millions of mid-size European cars.
AGM — Absorbent Glass Mat. The electrolyte lives in glass-fibre mats, not liquid. Handles deep cycling, high electrical loads and regenerative braking — standard equipment on most premium and recent Start-Stop cars.
The rule: never fit a lower technology than the car came with. Standard into a Start-Stop car fails early; EFB where AGM was specified isn't much better. Upwards (EFB → AGM) is generally fine.
Why the coding step matters
Recent cars manage charging based on the battery's declared type, capacity and age. Fit a new battery without registering it and the car charges the new unit on the old profile — undercharging AGM, or overcooking a smaller unit. The result is a "new" battery that behaves old within months. Registration/reset takes minutes with the right tool, and it's included in our replacement whenever the model requires it.
What it means at the roadside
Practically: when a Start-Stop battery dies in a car park in France, the fix isn't "any battery, quickly" — it's the correct EFB or AGM unit, fitted and registered, or you'll be doing this again soon. Our vans carry all three technologies, which is the entire point of the service. The early-warning signs of a dying unit are in the guide how long does a car battery last?
Start-Stop battery questions
Can I put a normal battery in my Start-Stop car to save money?
It will physically fit and the car will start — for a while. A flooded battery isn’t built for dozens of restarts per journey, so it fails early (often within a year) and can confuse the energy management meanwhile. Fit the technology the car was designed for: EFB where EFB was fitted, AGM where AGM was fitted.
Can I upgrade from EFB to AGM?
Usually yes (AGM tolerates the harder duty), and it’s sometimes sensible for taxi-like usage. Downgrading AGM to EFB is the direction that causes trouble. Either way the battery-management system must be told what’s fitted.
How do I know which type my car has?
The label on the battery says EFB or AGM; the handbook and the VIN also tell us. When you call, we identify the exact specification from the registration — you don’t need to crawl into the engine bay in a car park.
Why did my Start-Stop stop working before the car failed to start?
The car protects itself: when the battery weakens, the energy management quietly disables the stop-at-lights function to save what’s left. It’s the best early warning you’ll get — test the battery when you notice it.
Are AGM batteries worth the higher price?
For a car designed around AGM, it isn’t optional. The realistic comparison isn’t AGM vs cheap battery — it’s one correct AGM vs two wrong batteries and a strand on a cold morning.