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Yesterday I purchased a brand new, maintenance-free, 12 volt lead acid car battery. Specs: 47Ah and 450CCA.

Before I install it in my car, I measured the voltage with a catIII digital multimeter. It read only 12.33v. With the engine running, the reading is 14.2v (so the alternator works fine). After a 30min drive, the voltage was 12.72v right after I shut off the engine. After 8 hours sitting, the voltage was 12.38v.

Could this brand new battery be defective? The manufacturing date is OCT 2019 so for sure it must have been sitting on the shelf for quite a while. I also know that my car's drain is about 39mA-40mA.

What is the minimum voltage reading for a typical brand new battery?

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  • Welcome to Motor Vehicle Maintenance & Repair! Jun 9, 2020 at 22:33

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If the battery will start the car and is over (or in the neighborhood of) 12.5vdc, I doubt you have anything to worry about. The great thing about most battery manufacturers is, their warranty usually covers for at least three years. This means, if the battery does fail you, you shouldn't have a problem getting it replaced.

Really, what I'd do with it is, put it on a charger overnight and let it COMPLETELY charge. Then test the voltage again. A 30 minute drive may not have been enough to get it fully up to a nominal charge.

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  • Well, that was my first thought too. The store warranty is 2 years (14 day D.O.A) and the manufacturer warranty is 3 years. I have already ordered a slow 5A charger so I'll definitely try to charge it overnight when I get it. The point is though: if I manually charge it to 100% S.O.C. (around 12.75v) will the voltage stay above 12.6v, even after 20min-30min drives? Jun 9, 2020 at 22:46
  • But I'm still skeptical about that initial open-circuit voltage of 12.33v. In the past, most of my new batteries were charged to at least 12.6v. Jun 9, 2020 at 22:49
  • If the battery will start the car without issue, and the car will run without the electronics going crazy (which is what happens a lot of the time when the battery has low voltage), it should be just fine. Realistically, these are called a "12 volt battery" for a reason. Anything over the 12vdc is bonus. You may be used to a battery having 12.5+vdc, but really just because it's a little lower than that is nothing to worry about. If it had a bad cell in it, the voltage would be down around 10.5vdc which would make the electronics go batty. Jun 9, 2020 at 22:54
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    When was this "brand new" battery manufactured? Given the effect of Covid on the motor trade, it might have been sitting in the store you bought it from for 6 months without being charged. Give it long enough to recharge itself fully before you decide it is faulty.
    – alephzero
    Jun 9, 2020 at 23:38
  • Exide code: 9AC10E1. If I'm not mistaken, it should mean that my battery is manufactured in 2019, month 10. So October 2019. I know for sure that it was sitting for many months, I'm still not sure if it's accepting the charge as it should. I will retest it tomorrow and see. Jun 10, 2020 at 0:11
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Yesterday I purchased a brand new, maintenance-free, 12 volt lead acid car battery. Specs: 47Ah and 450CCA.

Lead-acid batteries that are "new" can actually be as much as six months old. They are no longer sold dry without electrolyte, requiring the user to fill the electrolyte. Instead, they are sold with electrolyte, which means they self-discharge on the shelf. For cost reasons, the seller doesn't recharge its inventory of batteries periodically, they are charged once on the factory, then they sit for as much as 6 months, then they are sold.

The self-discharging and being partially discharged for a period of as long as 6 months means that recharging it back is slow. A lead-acid battery that's in perfect condition will be able to be recharged in maybe 10 hours, no matter how fast charger you have, since in the end the charging current is not limited by the charger but rather by the battery.

A lead-acid battery that has been partially discharged for a period of 6 months can take as much as 30 hours to fully charge!

So what I would do is either of these two:

  • Drive the car at least 1000 km (not necessarily in one trip, but the trips need to be long enough, lots of 5-km trips won't recharge it fully) and measure the resting open circuit voltage again (after at least 3 hours of rest). Remember that the measurement temperature affects the results, so if you have a table of ideal battery voltages for 20 degrees Celsius, you should measure it at a time when the outdoor temperature is 20 degrees Celsius.

  • Charge it for at least 30 hours, one overnight charging isn't thus enough but two to three may be depending on the length of one overnight charge. Then let it rest for at least 3 hours. Then measure the open circuit voltage.

Remember that if you charge a battery for 30 hours, you really do need to use an intelligent microprocessor controlled charger. A traditional non microprocessor charger won't do, it'll damage the battery. Fortunately today even the cheapest chargers are usually microprocessor controlled.

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the battery is just sulfated, all you gotta do is take it to a professional for a refurbish... that or in other words, pump more than 14v thru it. a old laptop charger should have about 19v (cut top off and inner core is positve wire, outter mesh is negative wire). pop the caps off and keep a eye on it while it charges for a bit. odds re 20 min or so on a weak 19v signal will revive any sulfation you might have... there is no "bonus" lead acid is 2.1v per cell for a reason. having faulty cell can mean a explosive battery. so its good you know how to test voltage. if you have a careful steady hand you can measure the voltage of each cell. make sure each one is topped off with distilled water as well. ive done this to batteries that are over 10 years old and have one that i use to start my car every day... the capacity wont ever be quite the same but your voltage pressures should come right back (while under desulfation charge of 20 min to 1 hour max)

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