Bosch Alternator

Why is my car killing its batteries??
I have a 98 BMW M3 that has permanently depleted several gel-cell car batteries (Optima Yellow-tops & Die Hard Platinums).
The vehicle has two amplifiers and a capacitor, but the circuit breaker was disengaged (cutting off power to these components) during the entire lifespan of the last battery, which lasted only a month.
The vehicle contains a factory Bosch alternator, which I believe is 160 amp
What could be causing this problem??
The alternators job is to charge the battery. Sounds like the alternator’s bad.
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