Purchasing advice

Upgrade start-stop car battery:
Replace EFB with AGM?

Das Bild zeigt die Grafik zweier Batterien, wobei eine, durch einen Pfeil symbolisiert, durch die andere ersetzt wird.

Cars with a combustion engine and start-stop function require special start-stop batteries and there are also a few other things to consider when replacing them. You can find out how to proceed here and when you should decide to upgrade from EFB to AGM batteries in this article.

Das Bild zeigt die runde, grüne Grafik des Abschnitt 1.

Normal battery with start-stop: The problem

In a car without start-stop, the battery starts the engine once per journey and then it runs for the entire journey. In a start-stop car, it has to restart the engine every time it is switched on.

Tip:
This is a similar load to mega-short distances, such as a car for letter or parcel delivery that only drives from house to house and barely has time to recharge the battery in between. This is why the start-stop battery is also a good choice for some cars without a start-stop system.

The battery also supplies the power for the on-board electronics and electrical comfort features while the engine is off. And all this with the ever-increasing mechanization of cars. In cars without a start-stop function, this is done by the alternator - which is where its name comes from, by the way, because the very first cars were started with a hand crank and the alternator actually only looked after the lights.
Das Bild zeigt eine Grafik einer Batterie, die verschiedene elektronische Verbraucher versorgt.

Das Bild zeigt die runde, grüne Grafik des Abschnitt 2.

Start-stop batteries: EFB or AGM

Vehicles with a start-stop function need batteries that are designed for this use. They have to withstand an extremely high number of starts, many short charging processes and a high current output when stationary. This depends on which battery was originally installed:
Das Bild zeigt zwei schwarze Batteriekästen mit der Aufschrift intAct Start-Stop-Power EFB & AGM

For vehicles with simple start-stop systems in which an EFB start-stop battery was already installed, the intAct start-stop power EFB is suitable
For start-stop vehicles that recover energy during braking (recuperation) and have intelligent energy management systems, we recommend the intAct Start-Stop-Power AGM. Vehicles previously fitted with an EFB battery can also be equipped with an AGM battery.

Replace EFB with AGM or AGM with EFB - is that possible?

If the manufacturer has installed an EFB start-stop battery, it can be replaced with an EFB start-stop battery. An upgrade to AGM is also possible.
If the manufacturer has installed an AGM start-stop battery, it may only be replaced by an AGM start-stop battery. A downgrade to EFB is not possible.

A factory-fitted start-stop battery, regardless of the technology, must never be replaced by a non-start-stop battery.

Das Bild zeigt die runde, grüne Grafik des Abschnitt 3.

BEM: Key for start-stop

With the many demands placed on the battery in a car with a start-stop function, the battery could quickly go into deep discharge and suffer lasting damage because we are constantly taking out more than is coming back.
The graph shows the gradual deep discharge of a battery.

To prevent this, a battery energy management system (BEM) in the car monitors the status and charge of the battery and regulates the power output and charging currents, among other things. Some of this is noticeable to the driver: it only stops the engine when the battery charge is sufficient for another start. If there is a risk of overloading the battery, it warns you, for example, before switching on the air conditioning or parking heater. This not only protects the battery, but also saves electricity and fuel.
Das Bild zeigt das Zusammenspiel von Batterie-Energiemanagementsystem (BEM), Starterbatterie, Lichtmaschine und elektronischen Verbrauchern, symbolisiert durch ein Autoradio

Das Bild zeigt die runde, grüne Grafik des Abschnitt 4.

Change the start-stop battery yourself?

Since the start-stop battery and energy management system go hand in hand, changing the battery without registering or teaching it can lead to problems.
It is best to check the car's owner's manual or ask your trusted garage whether you can change the battery yourself.
Das Bild zeigt einen Schraubenschlüssel, der die Klemme am Minuspol einer Starterbatterie löst oder festzieht. Ein in einem roten Dreieck eingefassten Ausrufezeichen steht daneben.

Tip:
How big can the battery be? How do you measure correctly? How powerful should the battery be? We answer these questions in our buying guide for car batteries.
to our buying guide for car batteries

Das Bild zeigt die runde, grüne Grafik des Abschnitt 5.

intAct Start-Stop-Power EFB: Inexpensive alternative

Das Bild zeigt zwei schwarze Batteriekästen mit der Aufschrift intAct Start-Stop-Power EFB

Do you have a start-stop car in which an EFB battery was installed? Your car almost always stopped the engine when you stopped? You have not received any warnings or noticed any restrictions? Are you not planning any major changes to your car's electronic equipment? Then we clearly recommend the intAct Start-Stop Power EFB.

Tip: You can easily upgrade to the intAct Start-Stop Power AGM if you were not satisfied with the performance of your EFB battery.

What's inside the intAct Start-Stop Power EFB

The EFB battery (=enhanced flooded battery) is an improved wet battery, i.e. an improved lead-acid battery with liquid electrolyte. Other grid alloys, shapes and separator pockets and are designed to better withstand the special requirements of start-stop operation.
Das Bild zeigt die Gitterplatten, Separatoren und Säure aus dem Inneren einer nassen Blei-Säure-Batterie.

Increased service life: The service life of a battery is specified in charging cycles. However, a start-stop battery starts much more often than a normal car battery. An EFB battery manages around twice as many cycles as a normal starter battery
Better charge absorption: there is little time between starts to charge the battery. The grid structure and special separators are adapted accordingly.
Improved starting: start-stop batteries often have to start at a low charge. The grid alloy and shape help to provide the necessary currents even under these circumstances.

to our intAct Start-Stop Power EFB

Das Bild zeigt die runde, grüne Grafik des Abschnitt 6.

Recuperation and premium features: the intAct Start-Stop-Power AGM

If you have a car with a start-stop function in which an AGM start-stop battery was installed, you must use the intAct Start-Stop-Power AGM. Do not downgrade to EFB!

The AGM battery cuts a fine figure both as a 1:1 replacement and as an EFB upgrade.
We recommend it for cars with advanced energy management and energy recovery during braking (recuperation) as well as for sophisticated technical comfort equipment.

Even if you do not drive your car regularly, for long periods and at moderate temperatures, you should choose intAct Start-Stop-Power AGM.

What's inside the intAct Start-Stop Power AGM

The special feature of the AGM battery is its glass fiber fleece separators that are swollen by the electrolyte, from which it gets its name (AGM = absorbent glass mat). These swollen separators ensure their superiority over a classic lead-acid battery and an EFB battery in start-stop mode.
Das Bild zeigt die Grafik des Aufbaus vom inneren einer AGM-Batterie.

Even longer service life: batteries age every time they are started. They lose active material and electrolyte, which are needed to generate electricity. The glass fiber mats reduce this process and the AGM battery manages around three times as many cycles as a normal starter battery.
Better charge absorption: The AGM battery charges significantly better via the alternator during short journeys than a wet battery.
Improved starting: The fiberglass mats also make the AGM more efficient when starting. It reliably supplies the energy required for starting even when the state of charge is not optimal.

to our intAct Start-Stop Power AGM

Das Bild zeigt die runde, grüne Grafik des Abschnitt 7.

Conclusion: The right start-stop battery

If a start-stop battery is installed in your car, you can only replace it with a start-stop battery.
EFB batteries are suitable for simple start-stop systems, but only if an EFB battery was previously installed.
AGM batteries are the best choice for cars with advanced energy management, recuperation and premium features.
An upgrade from EFB to AGM is always possible. Downgrading from AGM to EFB is not possible.
It makes sense to have the battery replaced professionally if you want to benefit from the energy-saving possibilities and optimum service life thanks to the smooth interaction of battery and car.