Battery draining

I have a 1996 Buick Century that has a battery drain problem.  I have had it to a reputable mechanic twice in the last two months.  He has monitored the draw on the battery every hour or so for a whole day and has found no unusual draw, so the diagnosis is a "bad battery" and I come home with a new battery.  Since the last new battery a week ago, the car has been driven only once and I tried to start is today and it was dead again.  Any ideas on what is causing this problem?  I know it sounds strange, but there seems to be more problem when the car is parked in the sun.  When it is parked in the garage, the battery doesn't seem to get drained.  Are there some kind of light sensors on that car that could be causing the problem?  I have watched to make sure the interior light goes off when I park and get out and close the door.  I'm stumped.

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mailman

when you say the battery is dead, you mean no power what-so-ever? when you turn the key to start do the dash lights come on? has the alternator been checked out? its possible its not recharging the battery.

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Prove your connections, use a meter!
I promise, I'll behave!

I've experienced it being completely dead in the last couple of months, but today I got a little power, but not enough to start it.

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mailman

And, oh yes, the alternator checks out OK.  All the obvious things have been checked.

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mailman

3 things could be the problem.

bad battery
battery is being drained
bad alternator

these need to be check and rechecked until you find out which one is the problem. you've replaced the battery so i would look at the alternator and for excessive parasitic current (battery being drained).

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Prove your connections, use a meter!
I promise, I'll behave!

Since you've had the alternator tested and ruled that out, you should test for excessive battery drain.  You'll need a multimeter that can measure amperage.  With the car off and all the accessories off pull off your negative battery cable, and connect one lead of the meter to the cable, and the other lead to the battery post.  Be sure you start on the highest amperage setting. If your meter reads more than ~0.1A then something is dawing more current than it should. Begin by pulling fuses out of the fuse block one at a time until you see the amperage draw drop to 0.1A or less.  Be sure you turn the domelight off or remove the bulb before you do this. 

Once you determine which of the systems in the car is causing the drain, you'll have a much easier time narrowing it down to a specific component, especially if you can get your hands on a shop manual (Haynes, Chilton) with an electrical schematic.

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Life moves pretty fast; if you don't stop and look around once in a while; you could miss it.

Most mechanics are pretty bad with diagnosing electrical draw. Search the forum for specific instructions.

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Certified Security Specialist
Always check info with a digital multimeter.
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