My '92 325i had its original battery for 8 years...then it went bad.
Got a new one from dealer for $250 or so...less than a year later, it
went bad. But, for two months, and sadly, much wasted help from members
from this list trying to figure out what it was, it was just a bad
battery. My brother-in-law the mechanic said it must be a parasitic
drain...I spent a month pulling fuses, checking voltage, pulling bulbs,
checking to see if trunk light was one when closed (you get in with
someone you trust outside...no, not your wife! <grin>)...just a bad
battery.
Other simple things to check...alternator (if only 13.5 volts when
running, I suppose it could be that)...the ground on the
alternator...get a load test from a local shop or find instructions on
the web...I found them somewhere. All pointed nowhere...new battery
under warranty...problem solved.
Oh, btw, the light on the battery only indicates the one cell it's
hooked up on...one of the other cells could be bad...though yours is
indicating nothing.
So, as others have said, new batteries can fail. Sorry!
Cordially,
Doug
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