Battery or alternator,  what say you Oppo? 

"SaigaShooter - He's got an Impreza" (saigashooter) 12/16/2016 at 06:44 • Filed to: Repair, troubleshooting

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Good morning oppositelock, hoping you guys can throw some help my way this morning.

I’m trying to decide if I have a failing battery or alternator.

So heres the deal, yestetday it was - 9 f outside, car started a little hard, but that is to be expected, what I didnt expect is that when sitting at red lights on my way to work that the voltage gauge on the dash would drop to about 9-10 volts and a warning message would popup on the driver information center. If I hold the break and give it some gas to get the rpms up over 1500 or so, the volt meter climbs back up about 13 volts.

My first instinct was that the alternator is on its way out, but when I got to work I put the car in accessory power and sure enough, the volt meter was showing 10 volts from the battery.

So what do you guys think? Battery? Alternator? Both? Sell the hunk of crap and move to Arizona?

That Bastard Kurtis - An Attempt to Standardize My Username Across Platforms > SaigaShooter - He's got an Impreza 12/16/2016 at 06:49

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Could be a voltage regulator if its external. I don’t begrudge a battery anything it may do when it’s 9 degrees out, and if it weren’t taking a charge it might full field the alternator and make it put out 15v or so. My vote is alternator, or voltage regulator if external.

Tekamul > SaigaShooter - He's got an Impreza 12/16/2016 at 07:00

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Alternator or accessory belt not sufficiently turning the alternator. -9 can stress everything. I assume there were no odd noises.

RacinBob > SaigaShooter - He's got an Impreza 12/16/2016 at 07:37

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It’s hard to believe it would restart after dropping to 9 volts while running. If it’s really that low, it’s not the battery, it’s your alternator output is way below your consumption.

So, if it is really dropping that low, it might be a slipping belt. or maybe a bad water pump. I had a similar problem on a straight 6 mustang.. Dead battery. After changing regulator several times I happened to have the belt off and the water pump was stiff as hell. It turned but it was slipping under load. Never made a sound. The is a V belt drive problem, I don’t think a serpentine belt would slip like that.

The other possibility is you have a diode out in the alternator so that it kind of works, or maybe an engine ground issue. I would take it to an advanced auto or other place and get them to diagnose the charging system.

Problems like this show up in winter because you are driving with full defroster, headlights, wiper etc.

gmporschenut also a fan of hondas > SaigaShooter - He's got an Impreza 12/16/2016 at 08:02

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i’d get the battery tested at advance/autozone to remove that from the list of potential problems. cold can exaggerate a lot of minor stuff till it becomes noticeable.

Twingo Tamer - About to descend into project car hell. > SaigaShooter - He's got an Impreza 12/16/2016 at 08:03

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Id say battery.

SteveLehto > SaigaShooter - He's got an Impreza 12/16/2016 at 08:05

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Odds are the battery. The cold weather weeds out the weak ones.

merged-5876237249235911857-hrw8uc > SaigaShooter - He's got an Impreza 12/16/2016 at 08:08

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Looks like folks have suggested the alternator or battery. One other thing to check is the ground connections, likely not the problem, but will cause issues if it’s bad. But what you describe sure sounds like the alternator. But be warned, if you replace it, make sure to fully charge the battery or you will kill the new alternator too. A weak battery causes all sorts of problems, so does a bad ground and a failing alternator. Have you done a voltage check while the vehicle is running, you should 14 volts or more of the alternator is working properly.

BJ > SaigaShooter - He's got an Impreza 12/16/2016 at 08:12

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It sounds like an alternator problem, but I agree with Steve on this one: cold weather makes your nearly-dead old battery shine!

How old is the battery? If it’s 4+ years, chances are the cold weather has done it in. Have it tested by a local garage or parts store.

If charge problems persist after the new battery is installed, you have also have a bad alternator, or one of the other problem as described by the others here.

Rykilla303 > SaigaShooter - He's got an Impreza 12/16/2016 at 12:39

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as another said... time for testing at a parts store. But also check your cables and ground straps for tightness.