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Discussion Starter #1
First thing's first, I've used the search feature but haven't quite found an answer that best matches my issue. Not to say it doesn't exist; i just didn't find it. Been an active member of a Stella forum, so I know how frustrating it is when someone doesn't use the search function. With that out of the way, here's the situation:

About 2 months ago, the battery in my wife's car frequently wouldn't hold a charge over night. Her commute home is about 25 highway miles- ample time to charge it. I took the battery to be tested at the auto parts store and it failed. On two different machines, just to be sure.

So i get a new battery, drop it in and all is good. For about 2 months. Starts acting out. She drives to work, works 8 hours, drives home. Car sits overnight, won't start.

The lights all come on, etc, but the starter just clicks and the lights dim. Last night I get out the multimeter and check the voltage on the battery with the car off. Reads about 10+ volts. Something like 10.75v +/- a few decimal points.

Turn the car on like she normally would before starting and the battery drops 2 volts to 8+ volts. A starter typically needs 10-and-some-change volts to turn over.

Jump the car and it starts up. I turn everything off like headlights, dome lights, a/c, radio and unplug her phone charger which yields a reading of about 13.9volts. Pretty good. Turn everything back on, including the a/c and it drops down to about 13.8-13.75volts. Still good.

Hit the gas with a stick (in park and e-brake on), the volts fluctuate up a bit, but more or less stay about the same as the test above. Normal voltage out put of an alternator on a "typical" car is usually around 13.5 to 15v. So unless Smarts are different, I think this MIGHT rule out a faulty alternator. It doesn't 100%, but does yield some sense of confidence.

This all took about 5 minutes to test with the car running. I turn it off and do anther reading on the battery and the output is just a hair over 12v. The battery "charged" after just 5 minutes of running. Seems odd, and maybe it is, but we'll move along.

On a whim, I decide to start the car again. Turn everything on, including a/c, put the key in the start position. Output 10.9v. Cool. Should be enough. Turn the key over and the car fires up.

Not having anywhere to go, I decide to leave it for the night and check it in the morning. Lock it up and the headlights go off, dome light isn't on. The the multi-funtion yellow LCD display right under the speedo stays on for about 30 seconds and turns off. The only lights that stays on after everything turns off are the two blinks red LEDs on the center lock button and the tow-away button, that blink about every 3 seconds or so.

This morning, i check my readings. Off: the battery reads about 11.8...almost 12v. Turn everything on, a/c on, and it drops to 10.7v. A/c off, raises back up to about 10.9v. A/c back on and turn over the car and it fires up.

Everything seems normal. I'm wondering if there is a parasitic leach of power occurring some where besides the normal things like, radio/clock memory, alarm, etc. Or is it something else? Any thoughts to why some days the battery is dead over night?

Thanks in advance for your input.

Chris
 

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First off, you can't accurately load test a dead battery. If you take a recently discharged battery for testing, it will almost always fail. The proper way to test a battery is charge it first to full capacity, then load test it. This can take some time depending on the size of the battery and the size of the charger.

I'd do a parasitic drain test next, there are plenty of tutorials on line. Something in the car is drawing power out of the battery while it's sitting.

In short, the test involves a multimeter and removing fuses until the drain goes away. I've seen crazy items drain a battery, including bad alternators and stuck-on air condition compressor clutches, to name a few. Almost any electric motor in the car can draw power, yet not draw enough to spin, but draw enough to discharge the battery, given the right mode of failure.

Good luck.
 

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Discussion Starter #4
MB DNA - thank for the link. I'll take a look and it was a napa battery

Syndermann- The battery was charged...ish. You could drive the car and the battery would charge, but just not hold it over night. Seemed like just over a work day was about max. Of course it was the battery that came with the car. Even IF it was new when we got the car, which I doubt, it would have been close to on par for the life of it being over.

You're probably right about the parasitic leach/drain. What's odd is that the drain didn't occur last night. The car has been sitting at home today (my wife has off and i took my Element to work today). I'll take new readings when I get home and try to start it. If it starts AND you're right about the drain, but it's not happening all of the time then I'll have to figure out what event is causing it.

In the mean time, on to MB's link.

Thanks for the answers so far.
 

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If the system voltage is between 13.5 and 14 volts with the engine running and all the electrical loads on then the charging system is working normally. Note that the vehicle alternator is not made to repeatedly charge a badly discharged battery and continuing to do so can damage the alternator. The alternator is designed to replenish the engine starting current which normally occurs after 5 to 10 minutes driving time. After that time the alternator output should be typically be only powering the vehicle electrical load.

If your battery measures only 11.8 volts after the car sits overnight, the battery is discharged. Either the battery is bad or there is a parasitic drain on the system draining the battery. The object is to determine which is the case. A fully charged battery in good condition should measure 12.75 to 12.8 volts. If your battery is as low as you state it would take some time for it to fully charge while driving. I would disconnect it and fully charge it with a charger and see if it discharges overnight while disconnected. If it does, it is junk. New does not alway equate with good.

Now for the voodoo. Most people will remove fuses to find the circuit with the drain. This is not an ideal method. The electronic modules on the car must be allowed to time-out and go into a sleep mode prior to any testing. This can take from 10 minutes to 1 hour depending on the car. I would test for a parasitic drain by turning off the dome light and testing for voltage drop across the fuses. Any fuse with current flowing through it will show a small voltage drop. Once the circuit is identified more detailed testing can be done. This method reqiures a chart that shows the normal voltage drop for a given size fuse.

MOTOR Magazine Article | MOTOR Information Systems

Typical chart. http://www.angelfire.com/pa2/lberger/Vd_Fuse_Chart.pdf
 

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Just to make things even more interesting, some parasitic drains can be intermittent. You may need to check the vehicle multiple times until you get lucky and find the source.

Non critical fuses can be left out of the fuse panel to help narrow down the options for the drain. For example, if you remove the radio fuse for a few days and the battery stays charged, you've narrowed down the problem circuit.

Just be careful that you haven't disabled anything important. Fuses can run tandem circuits.
 
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