Why is acid stratification a problem?

The phenomenon of acid stratification occurs whenever batteries with liquid electrolyte are regularly discharged and recharged. The deeper a battery is discharged, the more rapidly acid stratification becomes a problem. However, in the long term a large number of flat cycles or deep discharge of the battery results in acid stratification. This is an uneven distribution of acid density within the battery cell. Acid with a higher concentration accumulates in the lower areas of the cell. Less concentrated electrolyte remains in the upper area. This causes three undesirable effects:

1. The highly concentrated acid in the lower part of the cell attacks the active mass of the battery and the lead grilles. This reduces the service life of the battery.

2. Because of acid stratification the open circuit voltage increases so that the battery management system incorrectly assumes that there is a higher charge level. This can cause additional stress on the battery due to an incorrect strategy by the battery management system (BMS), which causes premature battery failure.

3. Because of the increased open circuit voltage, charge acceptance is also drastically reduced, which can result in low charge so that the battery fails earlier.

4. Due to the different acid densities an internal charge transfer process occurs in the plates of the individual cells. As a result, part of the active mass is increasingly and permanently damaged due to sulfation and is no longer available. This reduces the available capacity and also dramatically reduces the cold start performance of the battery.

All three points cause premature battery failure and additional maintenance costs through more frequent battery replacement.

VARTA^® ProMotive EFB Batteries – a revolutionary solution

The solution which our engineers produced to eliminate the problem of acid stratification is the patented mixing element. The mixing element is located on the side of each cell and utilises natural movement of the vehicle to mix the acid. As the mixing element does not have any moving parts, wear is not a problem. Circulation of the electrolyte is achieved solely by steering movements, acceleration or braking and vibration of the vehicle. In this way, the electrolyte in the cell is constantly in motion. Due to a special design, the mixing element in the VARTA^® Promotive EFB battery utilises two basic physical principles (Link to Wikipedia article about 1: communicating vessels, 2: Bernoulli effect), to cause a turbulent flow within each cell. During the entire journey this flow ensures continuous circulation so that acid stratification does not occur during charging by the generator. In practice, with conventional wet batteries without a mixing element normal movement of the acid is not sufficient to prevent acid stratification.

Performance of VARTA^® ProMotive EFB batteries repeatedly confirmed

Various laboratory tests and field trials have shown that the VARTA^® Promotive EFB can meet much higher requirements than conventional wet batteries, which significantly increases their service life in the vehicle. The positive feedback from our original equipment manufacturers and the results of independent tests and reports also prove that with the Truck EFB we have a high performance solution for the requirements of long distance transport in our portfolio. The Truck EFB is a further example of the innovative strength of the VARTA^® Automotive brand. We develop battery solutions for the fleets of today and the future.