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Got a 2013 Cruze LT 2.4L. The charging system was acting up but never really had a battery light on. So I replaced the alternator. Now every time I start it up and look at the charging voltage it'll start at about 14.4 and then gradually go down. Sometimes for a while it'll stay at about 13.6 for different amounts of time but then eventually go down to 12.7 while driving. This is all with a brand new alternator and battery tested good. Any idea what causes this on and off like that? Still have never had a battery light come on and it's been doing this for awhile and I drive Uber so I go a decent distance and never had low battery starting condition, it always starts right up.
 

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This sounds normal. Loads vary and the charging system has a current sensor to adjust the battery load. Don't go changing anything until you can verify from GM technicians if you have a problem. I have a Honda that it actually shuts off the charging circuit when it see the battery fully charged. I have a scan gage and voltage will peak at about 14.2 then drop off to 12.2 until a load draws the battery voltage below 12.2 volts. I don't know what the reason is why engineers went this route. My guess is reduced load off the engine to improve fuel economy or reduce wear on the alternator.
 

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Well when i got the battery tested it was at 84% so it shouldn't be that low if it's lowering the charging so that it doesn't "overcharge it". It keeps going down and staying down
 

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This is normal for a Cruze. The alternator disengages under acceleration or when unneeded to help fuel economy.

Anything above 12.1V is acceptable to the Cruze's charging system. Below that, it will keep the alternator engaged and charging away.
 

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Reminds me of the good ol days before they started doing voltmeter gauges, just an ampere gauge showing basic charge/discharge....lol.

BTW, batteries will never be at "100%" while in service. Kind of like the reason for a battery tender. It's not a battery charger, but more so a battery maintainer because it is not designed to constantly put a charge into a battery. There's technical reasons about the inner workings of a battery that require this like keeping the plates and acid conditioned properly.

So basically, like everyone else says, don't ever look at your voltmeter because it's deceiving. Or, if you see anything below 12vdc and the charge light illuminated, then start to worry.
 
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