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Changed alternator but battery keeps going up and down

(2014 camaro 3.6 v6)Changed the alternator Wednesday and car worked fine. Thursday came and I was at a restaurant and the car gave me the battery saver mode on came back on. I checked the battery and it dropped to 11.9 v it usually stays at 14 something (I’ve never had to check it before so I’m not sure) I started driving around and it was just staying there. I drove some more it it started going back up to 14v. Friday I started it up again and it gave me that same battery saver mode on. I turn it off and on and it’s the same thing. It keeps saying it when I turn it on. The alternator was the problem but now I don’t know what is.


Ask your shop to do the basic alternator test. This is something many diy’er inclined folks can do themselves if they have a volt meter, pretty easy to do. Measure the voltage between the two battery posts. Before the first start of the day, it should be about 12.6 volts. Immediately after starting the engine, at idle it should be 14-15.5 volts. Turn everything electrical off you can when doing this test, no A/C, no headlights, no radiator fans spinning, etc. If your voltage readings are much different than those above, could indicate a faulty alternator, faulty battery, grounding, or computer problems.

Recent car designs – like your 2014 I imagine – tend to use an algorithm in the engine computer to determine the charging strategy. Rather than what used to be used, a solid-state voltage regular built into the alternator. Your car for example might not charge the battery at all if it determines the battery is already close to fully charged, and you are using the AC and the headlights on bright, and the stereo is cranked up full volume. Likewise, it might delay you from using the AC if it thinks the battery needs charging more than you need AC. So with the computer algorithm alternator strategy, you might see some voltages at the battery in certain circumstances you wouldn’t have seen in an older car using the voltage regulator method.

Where’d you get the replacement alt?
Some aftermarket sources sell a high percentage of junk.