Alternator or Battery?


Old 06-09-03, 05:06 AM
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Join Date: Feb 2003
Location: New Jersey
Posts: 229
Alternator or Battery?

Hi all,

The past 2 mornings the battery in my '99 Century has been dead. Yesterday, when I discovered it was dead, I put a charger on it and recharged it fully. I drove it around a good chunk of the day and it was fine.

This morning, dead again. I needed to get to work, so I jumped it with my wife's truck (she needs it today so I couldn't take it to work). When I got to work (20 miles), battery was fine (shut it off and it restarted). I unhooked the battery when I got here just in case there is a drain somewhere.

I have a DVOM, but haven't checked to see if there's a draw yet. Battery voltage is fine key off, engine off. I haven't checked the charging voltage, but the fact that it was dead in my driveway but fine once I got to work tells me it's charging.

My question, and I'm sorry it was a long time in coming, is will a bad alternator drain the battery? The car is smart enough to shut off any lights that are accidentally left on (interior, headlights, trunk, etc.) and there's nothing obvious that would be a drain. I know on my Fords, the alternators will short internally and kill the battery (some even flame out, which is fun - my Mustang burst into flames this way).

The brushes are making noise on the alternator, so I should probably replace it soon. Battery is of unknown vintage - it was in the car when I got it. I'm pretty sure it's new since the old one was demolished in the accident (the car is a rebuilt total). It looks new anyway.


Last edited by turbojimmy; 06-09-03 at 05:47 AM.
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Old 06-09-03, 08:32 AM
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Yes, a bad alternator will discharge a battery. Do an output check as noted in my "The Basics" below.

Also, you can hook a test light inbetween the battery terminal and battery and pull each fuse one at a time. The one that really dims the light is the problem circuit/drain.

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