Functional description

The AGM battery differs from conventional batteries in its substance-retaining behavior during charging.

When a vehicle battery is charged, the electrolysis process emits the gases oxygen and hydrogen. The two gases are non-toxic.

In a conventional wet lead calcium battery, the two gases hydrogen and oxygen are dissipated into the atmosphere. In an AGM battery, the two gases are converted back into water: The oxygen which is created at the positive electrode during charging passes through the permeable glass fibre fleece to the negative electrode. At the negative electrode the oxygen reacts with the arriving hydrogen ions in the electrolyte to form water (oxygen cycle). In this manner, the gas, and thus the electrolyte, is not lost.

Only in the event of an excessively high build-up of gas, i.e. excessively high pressure build-up (20 to 200 mbar), does the pressure relief valve discharge the gas (via a vent hole with hose). In this process, the pressure relief valve does not allow any oxygen in the air to enter.

Courtesy of BMW OF NORTH AMERICA, INC.