Battery at rest volatege 12.09 V

The battery is only about 8 months old, and this winter has been unusually cold in Northeast, and continues to be cold. This morning, I discovered my car batter at rest is only 12.09. If I start the engine, it goes up to about 14.25 due to alternator output voltage. Back about 8 months ago, output with engine on was only about 13.5 so it seems like alternator is good and is able to adjust the output by itself based on battery charge level??? I turn off the engine, and wait a few minutes, battery at rest goes back down to about 12.09. It is still starting the car, but how could a 8 month old battery discharge so quickly? How likely is it this well known parts store will honor the 2 year warranty on the battery? Your opinions? Thanks.

It depends on how long the battery sat on the shelf before you bought it.

When a battery sits idle for a long period of time, it can sulfate. And that can determine how well a battery takes a charge and keeps the charge.


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Battery sat on the shelf 4 months after the date of manufacturing. This name brand parts store claimed batteries have 10 month on the self life. My concern with warranty is once drive the car to the parts store, the battery will get charged, and they ask you to pull up to the curve and it may not be possible to sit on the curve waiting for the battery voltage to go down for them to see 12.09V.

It doesn’t take long for a battery to sulfate.


12.09 volts is too low for a new battery. 14.25 is great for the alternator. You might take it inside and check it again when warm.

Take it back and have them check it on a load tester. Heck, I’d be thinking of replacing my battery if winter was coming and i got those readings.

Your battery state of charge is low, possibly due to short trips and periods of inactivity. Recharge the battery, this is not a warranty issue.

Yep, I think they would say the battery is fine. May not be great but has not failed for replacement. I agree to charge it first and see what happens. After mine sat for a week and its cold, I’ve been charging mine just to make sure. When I asked about how fresh the batteries were when I bought my last Delco, they said they get a truck in every day, so batteries don’t sit for more than a week.

You want to do a battery conductance test. Because a battery conductance test doesn’t require that the battery be fully charged.

Where with a load test, the battery must be fully charged.

So, if the battery doesn’t hold a full charge, a load test is useless.


You are correct. I was told it’s the cold weather that did it to everybody and battery simply needs to be recharged, and everyone was fine after recharging… I recharged it fully to 12.69V. I then had my dinner and took a shower. It then went down to 12.45V. Any thoughts? Unless the battery flat out dies and you get stranded and have to take it out of the car and can bring it into the store in your hands, I wouldn’t count on warranty. Should I simply keep an eye on it periodically and recharge as needed? Battery is 8 months old. I was told the on shelf life of battery is 18 months. After 18 months, they can’t sell it.

Sounds like you partially charged the battery and measured the surface charge.

Depending on the battery’s state and the charger used it can take 10 to 12 hours to fully charge a battery.

I agree with Tester though that you really need a test of the cold cranking amps. Its been cold here in Minnesota and both of my batteries are down about 50 CCA from October when I last tested them. I don’t think its any big thing considering they sat with little activity or short trips, so just charging them. Both two years old and I suspect I’ll probably replace them after 3 years. Probably ok but voltage alone doesn’t give the whole story.

I am going by the car batteryworld chart and the indicator light of my charger when I said fully charged Perhaps my charger is faulty? If you could advise how I can not measure the surface charge, that will be helpful. What I did was to place the end of positive and negative needles of multi-meter onto the top of positive and negative probes, respectively, with the engine off.

I see two ways to go here: 1. Just buy a new really good battery with more than a 2 year warranty. 2. Have Amazon send you a emergency battery jump pack and keep it charged and in car.

Yes, I think a portable jump starter is a worth the investment for all of us. Thanks for the tip. =) Well, as for the warranty, the battery is 8 months old and has 1 year and 4 months of warranty left.

Just wait for the surface charge to dissipate as you did or you can switch on the headlights for 15 seconds to remove the surface charge.

If you are using an automatic battery charger that switches off when it detects a full charge use the lowest setting for a deeper charge.

You might have someone turn the engine over while you check the battery voltage while the engine is cranking. How much does the voltage drop?
You may want to check the accuracy of your voltmeter. Take a fresh battery anything from a AAA to a D cell. Your voltmeter should read about 1.64 volts.

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If the battery still cranks the engine ok, you don’t need to replace the battery. The low voltage could be

  • volt meter is inaccurate
  • battery not being fully charged due to short trip and infrequent driving
  • battery post connections are corroded/loose
  • something in the car is turning on and putting a drain on the battery overnight

Connect the voltmeter. Remove the fuel pump relay. Crank the engine for 10 seconds or so. The battery reading should stay at or above 10.5 volts.

If it goes into the 9s then the battery is on shaky ground. Being new means nothing I’ve seen and even bought batteries that were no good at a young age. One of them completely died the day after I bought it… :frowning:

You can test the density of the electrolyte with a cheap hygrometer.

What’s the voltage an hour after you drive it?

Because mine sits for months at a time I have a battery booster.

I had the battery charged at the parts store in case my charger is not good. The highest it will charge was 12.70V. However, the same problem continues. The next day at rest voltage was around 12.08V to12.14V which might be a little better than 12.09V I discovered at the beginning of the week. The alternator output is about 14.25V. After I idle the engine or drive the car a bit, then the battery at rest voltage is at around 12.53V immediately after turning off the engine. However, in about 30 min, it goes down to about 12.08 to 12.14V. Should I just keep charging the battery about once a month and hope it will last about a year? If I charge the battery every month, can that damage the battery or any computer components in the car?