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I have a 2009 Chevrolet Aveo that I bought new from the dealer.

Today I was running errands around town and just as I was about the get on the highway to head home, the battery light and emergency brake light turned on. As I was driving home, the electrical components in the car started going out one-by-one. First the tachometer went to zero, then the fuel and temperature gauges, then the windshield wipers started moving slowly, the radio turned off, then all off the lights on the dash. Each one of these shut off 30-60 seconds after the one before it. As I was pulling off the highway and onto my street (which is a hill) the engine started losing power. I was able to crawl at a snail's pace about halfway to my house (50 meters) before the engine died. I put it in reverse and compression started it, put the emergency brake on and shifted to neutral. After I shifted it to neutral, some of the components in the car started turning back on and off and the RPM increased. After letting it sit for a few minutes I was able to crawl the rest of the way home (another 50 meters).

After getting home I took my girlfriend's car back to town and got a multimeter. When I got home about 2 hours later I tested the battery with the engine off. It read 12.18 volts DC. To my surprise, when I turned the ignition the car started right up with no battery light and all the electrical components working. After about 20 seconds the electrical components started turning off. I was able to test the battery with the engine running and it jumped between 3-6 vdc for a few seconds before the car sputtered and shut off.

I am thinking alternator or connection problem, but I really don't have much experience with this kind of thing. Any ideas?

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This sounds like an alternator problem to me. If you have the means, pull the alternator and take to an AutoZone, Pep Boys, or the like. They will test it for free for you. The reason I suggest an alternator, is this is typical behavior when the alternator is dieing, where your electrical components start shutting off as you are going along. Also, if the battery is good, you'll see where it will incur a "rebound" effect (the way I think of it anyway), where while you were using the vehicle, the voltage may drop down, but the once the vehicle is off, the battery voltage will rebound back up a ways. It isn't that it is recharged, just that it will recover some of its voltage after a large power draw.

If you want to test this at home, the easiest way I have found to do it is to get the battery fully charged (13.1+ vdc). Start the engine and let it run. Keep the multi-meter on the battery posts and watch the voltage. You'll see the volts slowly sink down as the engine and accessories eat up the charge in the battery.

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When testing your battery, you must check the voltage across the actual battery posts. The posts are the lead posts coming out of the casing of the battery. Do not measure using the leads coming off of the battery. If, using the posts, your voltage is below 12.+ volts, and you have a known good voltmeter then you have a defective battery. If the voltage is at 12.+ volts across the posts, but very much lower on the cables as you have described, you have a cabling fault or shorting alternator. Ideally you should fully charge a battery 'off of the vehicle' before testing it to eliminate any effect from a fault that may have discharged it.

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