A battery does not on its own, spill acid out the vent holes unless its been overfilled or the case is leaking (cracked) Acid loss is usually uncontrolled voltage or amperage caused by a faulty Alternator or voltage regulator. In rare cases a cell can be shorted within the battery and that could cause an extended high charging rate from the alternator to compensate for the cell. Now that you've replaced the battery, you will know soon enough if it was the prior battery or a charging issue.

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.