When a battery is charged and discharged, water contained in the electrolyte is decomposed, generating hydrogen and oxygen gases. These gases are vented out of the battery through the exhaust vent tube to prevent potentially damaging high pressure gas accumulation. Every exhaust tube comes with a small slit at each end. The reason for this slit is to release the gas, in the event that the bottom of the tube gets clogged by road debris. For this reason, it is most important to make sure the slit at the top near the battery is functioning properly. As as side note, always be sure to remove the small red sealed tube when installing the battery. Never put this red tube back on to the battery after it is activated. Gases built up in a battery that is not allowed to vent can cause serious damage, and possible injury, if the battery bursts.