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What could be the issue? 3 alternators and all have the same issue, charge for 5 minutes after start up at 14.7, before gradually decreasing to 12.8! My previous battery was killed by this, now my new battery looks like it will have the same fate if I don't fix this!

I understand the alternator voltage regulator is in the alternator itself but why wont my car excite the alt to keep it charging? My new battery has gone from 13.0v float to 12.5 in a week. Also I have upgraded to a mechman alt and it hasthe same issue!
 

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Someone correct me if I'm wrong...but doesn't the voltage demand come from the ECM/PCM? I know the regulator is in the alternator, but I thought it was controlled through the ECM still. Could be wrong though. At any rate, I would try cleaning all the related grounds and make sure they are tight. Trace all the wires coming from the alternator as best as possible, making sure there are no breaks or loose connections.
 

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Reubenswinks thanks, that's what I was afraid of. Do you think jumping the alternator plug would excite the alternator 24/7? Maybe leaving it in there for a day to charge the new batt to keep it from discharging?
 

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Reubenswinks thanks, that's what I was afraid of. Do you think jumping the alternator plug would excite the alternator 24/7? Maybe leaving it in there for a day to charge the new batt to keep it from discharging?
I would not do that. I have no idea what voltages those alternators are capable of when not regulated. You stand the chance of over charging or damaging electronics. As a temporary solution I would buy a battery tender and plug it in every night.
 

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What could be the issue? 3 alternators and all have the same issue, charge for 5 minutes after start up at 14.7, before gradually decreasing to 12.8! My previous battery was killed by this, now my new battery looks like it will have the same fate if I don't fix this!
Besides this observation of the voltage, are you having any other symptoms with the new battery? Are you getting no-crank conditions requiring a jump?

I poked around on this some, and found that the BCM monitors the battery current and sends that info to the ECM which in turn controls the alternator.

The voltage levels you cite are all within the normal operating range for the system. It's normal for the voltage to go up and down.

If you'll PM me your email address, I'll send you the "charging system description" I found.

Doug

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Discussion Starter #6
Besides this observation of the voltage, are you having any other symptoms with the new battery? Are you getting no-crank conditions requiring a jump?

I poked around on this some, and found that the BCM monitors the battery current and sends that info to the ECM which in turn controls the alternator.

The voltage levels you cite are all within the normal operating range for the system. It's normal for the voltage to go up and down.

If you'll PM me your email address, I'll send you the "charging system description" I found.

Doug

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After new battery went in no sluggish start, before it would. It was an agm battery too.
 

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After new battery went in no sluggish start, before it would. It was an agm battery too.
I emailed the info.

Not sure why there was an AGM in there. I've seen them used on diesel Cruzes, but I think only on diesels. Not sure how adaptive the Impala charging system is, but AGM batteries, from what little I know, have a wider voltage range as part of normal operation, including charge cycle. They get discharged to lower levels before re-charging, and are able to tolerate that well. Here's an article about AGMs.

That type of operation will wear out a normal lead acid battery.

Reading the Impala charging system description, I saw no mention of AGM, so I think your Impala is set up for normal (flooded) lead acid batteries. And that should have posed no problems to an AGM. (I think it's only a problem the other way around, when the charging system is for AGMs but the battery is the traditional flooded cell.)

Anyway, as long as you're not having any starting / weak battery issues, I think you're good to go now.

Doug

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