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2012 Elantra battery running at 11.7 volts #5332868 01/26/20 03:31 PM
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schuylkill Offline OP
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Driving home today and my battery light came on. I have an ultragauge and it showed 11.73 volts, held there pretty steady for about 15 mile ride home. The car starts up. Battery is about 2 years old I believe. Original alternator and voltage regulator, just passed 334K miles. Regulator is external on the alternator. How can I diagnose what is failing?


09 Elantra 32K Bulk Toyota OE
12 Elantra GLS manual 299K TGMO Fram Ultra
Re: 2012 Elantra battery running at 11.7 volts [Re: schuylkill] #5332873 01/26/20 03:41 PM
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zzyzzx Offline
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Check resistance of the rotor. There is at least a chance that the brushes are worn out.

Re: 2012 Elantra battery running at 11.7 volts [Re: schuylkill] #5332886 01/26/20 03:52 PM
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MasterSolenoid Offline
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I had a similar problem recently.
Here is the thread:

https://www.bobistheoilguy.com/foru...7/alternator-battery-problem#Post5243327

I installed a 'new' Alternator and all is well.


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Re: 2012 Elantra battery running at 11.7 volts [Re: schuylkill] #5332887 01/26/20 03:53 PM
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JHZR2 Offline
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Definitely low. I’d want to know what your battery voltage is with the engine off... if it’s in the 10v range, then the battery has a shorted cell and the alternator is unable to source the current that the battery is “burning” up.

I’d suspect at the age you mention, it’s more just some worn components.

Is there a replaceable voltage regulator? That would be my first look.

Re: 2012 Elantra battery running at 11.7 volts [Re: schuylkill] #5332926 01/26/20 04:42 PM
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atikovi Offline
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Either get a shop manual or online access to the repair information to run the diagnostics. Or pull the alternator and get it tested.

Re: 2012 Elantra battery running at 11.7 volts [Re: schuylkill] #5332928 01/26/20 04:43 PM
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eljefino Offline
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There's a chance that an external regulator has a diagnostic method that full-fields the alternator so it could make 16 volts, proving which part is at fault. Dig up your repair manual.

Re: 2012 Elantra battery running at 11.7 volts [Re: schuylkill] #5332933 01/26/20 04:51 PM
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schuylkill Offline OP
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With engine off 12.3 volts. Checked battery negative to positive post on regulator with engine running and reads 11.7 volts. $200 for Denso alternator and $150 for regulator at Rock Auto. Denso at NAPA is $378. What to do what to do. Could it be the brushes in the regulator are worn?


09 Elantra 32K Bulk Toyota OE
12 Elantra GLS manual 299K TGMO Fram Ultra
Re: 2012 Elantra battery running at 11.7 volts [Re: schuylkill] #5332938 01/26/20 04:54 PM
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spasm3 Offline
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I would unhook the battery cables and charge it. See what it will charge to. And see if it will hold that charge overnight. If it will hold a 12.6 overnight disconnected from the car , then i think you will need an alternator.

Last edited by spasm3; 01/26/20 04:54 PM.

13 elantra 81k 5w30 synpwr
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Re: 2012 Elantra battery running at 11.7 volts [Re: schuylkill] #5332942 01/26/20 04:56 PM
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Rand Offline
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most likely the alternator.. just get a new one with internal regulator for 105, or the new denso(includes regulator) for 199


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Re: 2012 Elantra battery running at 11.7 volts [Re: schuylkill] #5332944 01/26/20 05:01 PM
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schuylkill Offline OP
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Good news is on Rock Auto states regulator is internal so would only need to purchase alternator. Remy rebuilt is $135 think I may pull trigger on it depending on shipping cost and time, still looking into AA deals. Regulator looks to be external and it can be bought separately but is included with alternator purchase.


09 Elantra 32K Bulk Toyota OE
12 Elantra GLS manual 299K TGMO Fram Ultra
Re: 2012 Elantra battery running at 11.7 volts [Re: schuylkill] #5332948 01/26/20 05:04 PM
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Chris142 Offline
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Full field the alternator. If it charges the regulator is bad. With that many miles I would guess that the alternator brushes wore out.

Last edited by Chris142; 01/26/20 05:05 PM.

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Re: 2012 Elantra battery running at 11.7 volts [Re: schuylkill] #5332962 01/26/20 05:14 PM
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spasm3 Offline
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Originally Posted by schuylkill
Good news is on Rock Auto states regulator is internal so would only need to purchase alternator. Remy rebuilt is $135 think I may pull trigger on it depending on shipping cost and time, still looking into AA deals. Regulator looks to be external and it can be bought separately but is included with alternator purchase.


The alternator is $185, plus shipping to you. core is $50 and if i'm not mistaken, you pay to ship the core back to them. So its more that $135 depending on the ship to you cost and the core shipping cost.

Last edited by spasm3; 01/26/20 05:15 PM.

13 elantra 81k 5w30 synpwr
03 chevy avalanche 83k synpwr 5w30
17 mazda cx-5 17000 miles synpwr 5w30
Re: 2012 Elantra battery running at 11.7 volts [Re: schuylkill] #5332964 01/26/20 05:17 PM
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I bought a used OEM alternator for $25 for my 05 Accord about a year ago. Works great and was cheap. I'd say there is a good chance it will outlive a rebuilt china one.

Found it on car-part.com at a local salvage yard.


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Re: 2012 Elantra battery running at 11.7 volts [Re: schuylkill] #5332969 01/26/20 05:19 PM
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Isn't the best alternator a rebuilt one from a local alternator/starter service shop? I hear they often replace components with parts that are higher quality than the originals. Maybe this isn't true for all shops.


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Re: 2012 Elantra battery running at 11.7 volts [Re: jayjr1105] #5333001 01/26/20 05:49 PM
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atikovi Offline
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Originally Posted by jayjr1105
Isn't the best alternator a rebuilt one from a local alternator/starter service shop?


Those went away years ago with the advent of the internet and new Chinese models for $50. Nobody would pay the $150 to rebuild theirs.

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