Mercedes E220 Aux Battery-Start-Stop

AGM versus EFB: Which one should you be using?

AGM versus EFB

AGM versus EFB
AGM versus EFB

AGM versus EFB

So, it’s probably about ten years since the first stop-start vehicles became production vehicles. Consequently, the batteries for these vehicles are now required to be changed. Motorists with these start-stop vehicles have become very confused as regards which battery to replace their old batteries. Confusion surrounds the two new technologies in car batteries that were originally fitted to these vehicles! The AGM and the EFB Batteries

However, I will try to explain the difference and the correct fitments for your car or van. Because of environmental issues, there are now more than 70% of new cars that are equipped with an energy-saving Start-Stop system. Car manufacturers developed this system along with battery manufacturers. So, the Start-Stop system enables the vehicle to switch off the engine when it comes to a halt! For example, at traffic lights and road intersections.

Along with modern fuel injection engines combined with an onboard computer, there are significant fuel savings. Therefore, if the engine is not running, this also means lower emissions coming from the vehicle. Time this by the number of vehicles using the same system, and significant savings will be made both in fuel consumption (also saving the vehicle owners some money) and greenhouse gases. It is possible to cut CO2 emissions by as much as 8%.

pressing his start stop button
© Can Stock Photo / Bignai

Start-Stop system batteries face higher demands

It’s not rocket science, but the start-stop system in most cars now will place the battery in a higher-demand situation. A different type of battery than the regular “lead acid starter battery” had to be developed. So, more power was required to facilitate higher cycle stability. This new type of battery has to provide the car with enough power to restart the engine on multiple occasions. Also, these vehicles have more electrical loads to cope with! once again requiring a different type of battery.

The AGM battery was developed to cope with vehicles equipped with “energy recovery”. So, this simply means that energy is recovered from the vehicle’s braking system. When you slow down or brake, some of the kinetic energy from your vehicle is lost. The energy recovery process recovers some of this energy. When this process is happening, the car alternator is put under extra stress. So, causing the voltage to be increased accelerates the charging process!

Consequently, the alternator converts the “kinetic energy” into electricity. To simplify things, then the whole process works similar to pushing a bicycle dynamo. I am trying not to be too technical, but fitting the correct type of battery is very important.

AGM battery (Absorbed Glass Matting)

  • Starter battery and on-board battery for start-stop vehicles with the highest energy requirements and brake energy recovery
  • for middle- and upper-class vehicles up to luxury-class
  • as many as 360,000 engine starts

As a result, AGM starter batteries have triple the cycle strength of conventional starter batteries and the highest vibration resistance in continuous operation. Because the electrolyte is bound in a glass mat (Absorbent Glass Mat), it is leak-proof.

EFB battery

  • Starter battery and on-board battery for vehicles with high energy requirements and simpler start-stop systems
  • for small cars up to upper middle class
  • as many as 270,000 engine starts

The EFB battery has high vibration resistance and twice the cycle life (when compared to conventional starter batteries). Furthermore, the carbon additives lead to the charging time being significantly reduced! The EFB battery is also used in the commercial vehicle battery sector, especially for long-distance lorries, where maximum energy consumption is required due to increasing comfort functions and extreme vibration resistance in the case of integral rear mounting of the battery.

Exide EK950-95Ah-AGM-Start-Stop-017 Battery

Accordingly, if your car was fitted with an EFB battery from the beginning as a new car, then it should be replaced by another EFB battery. However, as an upgrade, it could be fitted with an AGM battery. Importantly, the EFB and replacement AGM should be the exact same size with similar performance. If the replacement battery has a slightly different capacity or cold start performance, then this should be fine to fit.

So, if your car or van is fitted with an AGM battery as standard, it is imperative to replace it with a replacement AGM battery again. and not an EFB battery. Of course, in identical housing and with a similar performance class.

I really do hope that this will help ! Ideally, replace like for like if possible. The car’s computer system eventually rejected the incorrect battery after we had issues with online customers who cut corners.

eric roberts
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