I understand your calculations, but it really doesn't work that way. If the battery was supplying current constantly your lights would dim terribly at night.
More likely there's a constant draw on the battery when the engine's off. I'd suspect the alarm if it's new.
If you have a DMM with a 10 amp DC scale, you can put the meter in series with the battery cable and check to see if there's constant current being drawn (arm the alarm too). Any more than a few milliamps means there's a problem.
1999 Buick Park Ave Ultra
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