Service life of AGM battery
WARNING: This page is about a different car, the 2010 BMW 550i, 2009 BMW 550i, and 2008 BMW 550i. However, it is still accessible from the selected car via links, so may be relevant.
Unlike the previously used lead calcium batteries, the sulfuric acid contained in batteries with fleece technology is not self-contained in the battery housing.
Instead, the sulfuric acid is 100 % bound up in glass fibre fleece mats (separators). Thus, no acid can escape if the battery housing is damaged. In addition, the AGM battery is sealed gas-tight. This is possible because the gases are converted back into water as a result of the separator permeability.