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The very short version of the story is my battery will not charge/hold a charge. The car (2009 9-3 Aero SS) has been working fine until recently. Drove to a location about 100 miles away. After taking care of business I jumped in the car to go home and the battery was so dead that I couldn't get the key out. Someone stopped to help me out and got the car jumped ... started first try. On my drive home, I had my ScanGuage II running and monitored the voltage. It was 13.7v with nothing on and dropped to 12.5 with lights, fogs, radio, and AC on. This trip should have fully charged the battery.

After getting home, I turned the car off ... and then tried to start it again. Nope ... dead and locked the key in the ignition again. Called AAA out and they tested the system. They say the battery is good but detected "excessive ripple". No idea what that really means, but guessing rectifier is faulty and not normalizing the voltage from AC to DC. The next day I went out to put the battery on a charger to see if it would hold a charge and noticed the negative battery cable was very warm ... clearly flowing a lot of juice.

So, where is the likely problem? If I had a job I would probably take it to the shop to be fixed, but Looks like I need to do this on my own.
 

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Sounds like you need an alternator. 12.5v with all the accessories on is way too low. Im at 14.4v on a cold start. Under 13v means alternator no bueno. Im pretty sure if ur getting excessive ripple it means the alt is converting the ac to dc - so a bad diode i think-anyway bad alternator. Be sure to get your battery load tested or retested at an auto parts store after you put in the new alt. The bad batt could kill the new alt. Batt connections should be clean and tight. Rock auto for the alt. Get one with a long warranty. My bosch quit before the year was over. The swap is a medium difficulty job in my opinion. Accesory belt needs to come off. Oh yeah, get a new one of those, theyre like $6. Good luck. Another thing, when you have the batt out you can clean off the ground connection under the batt tray. All elec connections clean and tight!
 

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Sounds like you need an alternator. 12.5v with all the accessories on is way too low. Im at 14.4v on a cold start. Under 13v means alternator no bueno. Im pretty sure if ur getting excessive ripple it means the alt is converting the ac to dc - so a bad diode i think-anyway bad alternator. Be sure to get your battery load tested or retested at an auto parts store after you put in the new alt. The bad batt could kill the new alt. Batt connections should be clean and tight. Rock auto for the alt. Get one with a long warranty. My bosch quit before the year was over. The swap is a medium difficulty job in my opinion. Accesory belt needs to come off. Oh yeah, get a new one of those, theyre like $6. Good luck. Another thing, when you have the batt out you can clean off the ground connection under the batt tray. All elec connections clean and tight!
Oops, i meant isnt converting one phase of ac to dc. You can look it up - excess ac ripple. Try to fluke website.

Not sure how to edit on my phone
 

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The combination of "so dead" and "started first try" is a disconnect. Try clean the battery terminals. It may not fix it but it's easy and cheap.

I do agree that 12.5 when running is low. Does it go to 13.7 if the engine is revved up a bit?
 

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Charging volt should be 14.4v-14.6v-ish..if the battery is more than 4-5yrs old then it's time to replace even more so on the V6 due to the placement near the turbo..

How the hell can you test a dead battery..
 

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Discussion Starter #6
The combination of "so dead" and "started first try" is a disconnect. Try clean the battery terminals. It may not fix it but it's easy and cheap.

I do agree that 12.5 when running is low. Does it go to 13.7 if the engine is revved up a bit?
It started first try AFTER it was jumped. The battery has been replaced 3 times since the first event.
 

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Discussion Starter #7
Charging volt should be 14.4v-14.6v-ish..if the battery is more than 4-5yrs old then it's time to replace even more so on the V6 due to the placement near the turbo..

How the hell can you test a dead battery..
You are right, the heat of the v6 engine kills batteries and I've been through several. However, this is something new and the current battery has been swapped out three times in the last week. I am guessing alternator or regulator.
 
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