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I recently purchased a brand new 12 volt AGM motorcycle battery.

When I got it home I measured it with my volt meter and it read 11.81 volts. I took the battery back to the bike shop and tried to explain to them that this battery was in extremely poor state of charge for a brand new battery. They tried to replace it with another one which also read 11.9 volts, which I also politely pointed out was completely discharged and not fit for sale.

After the ensuing verbal spat, telling me in not so uncertain terms what a freak I was and that they'd seen plenty of batteries come back to perfectly serviceable life after dropping to two volts. I got my refund but it wasn't a pleasant experience.

I've bought more than a few batteries over the years and have learnt that it's a good idea to take a volt meter along to test a battery before I buy it. My cut off point is about 12.4 volts, anything lower I won't buy it.

Am I being a bit over zealous, what do you think a respectable voltage is for a brand new 12 volt battery? I like to see at least 12.6 volts.

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    Did you try and charge the battery? Batteries lose power over time while sitting on the shelf. If the battery will not hold a charge, then you have an issue. Just because it's below 12vdc when you get it, doesn't make it a bad battery. If you put a charger on it and it still doesn't come above 12vdc, then you might have an issue. Jul 5, 2017 at 13:33
  • Yes I did and it accepted a full charge, but that did not inspire confidence, mostly my experience is with flooded lead acid, in particular deep cycle as opposed to AGM. I would never trust a flooded battery that was a) brand new and b) in a severely discharged state. See my links to battery university
    – Ian Oakes
    Jul 5, 2017 at 13:59
  • I would actually say that batteryuniversity.com/learn/article/lead_based_batteries is the best link, as it says "The battery must always be stored at full state-of-charge. Low charge causes sulfation, a condition that robs the battery of performance."
    – juhist
    Jul 5, 2017 at 14:01
  • So if we can trust the battery university, their table outlining state of charge for a 12 volt battery shows at 11.89 volt the battery is at 0% charge. If we then consider that the self discharge rate for an AGM battery is somewhere between 1 and 3% per month, the battery had been sitting on the shelf at least 30 months. The sticker on top of the battery also suggested it was manufactured in 2014.
    – Ian Oakes
    Jul 5, 2017 at 21:59

2 Answers 2

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It's quite possible there's nothing wrong with the batteries. Batteries do lose charge over time. Frequently, a car battery will be around 13.5V or higher, but if the charge drops to 90% (normal shelf storage percentage), the voltage will drop to ~12.6 to 12.8. (Source)

It will then usually drop steadily to 11.5 or something around there, at which point the voltage stays relatively steady until the voltage drops below 10%, at which point the battery is empty enough that it can cause serious damage.

You write that the battery is at 11.8 or 11.9. I'm guessing they've over stored their batteries a bit, but there's almost definitely no permanent damage to the battery from that. If you want to really play it safe, there's no harm going to another garage where the batteries are somewhat newer, but 11.8 volts is probably around an 80% charge. While this isn't the norm, IMHO, it's not unacceptable.

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  • I would actually disagree with the statement that there's almost definitely no permanent damage to the battery from sitting without full charge. Lead acid batteries degrade exactly from that: by sitting without full charge. So, if you have an unused battery, charge it often! If you accidentally drain all charge from your battery, charge it immediately! However, if the battery wasn't completely empty when sitting on the shelf, I guess it may still retain 90% or so of its capacity to hold charge.
    – juhist
    Jul 5, 2017 at 13:49
  • My feelings exactly
    – Ian Oakes
    Jul 5, 2017 at 13:54
  • @juhist, absolutely true, and I would disagree that there is no permanent damage to the battery from sitting without full charge too, except that I'm guessing that the battery was probably around 80% charge. It's not ideal, and like I said, if you want to play it safe, go to another garage. But I've left batteries without prior charging (except normal vehicle running), with no charger attached for 6-8 months straight every year for 5 years on end and had the batteries still crank just fine. But good points, thanks for noting. :)
    – anonymous2
    Jul 5, 2017 at 15:12
  • Yes, agree with the 6 months figure. Battery University says 6 months without charging is ok but for longer intervals you should apply topping up charge: batteryuniversity.com/learn/article/… ...so the question is of course was the OP's battery older than 6 months?
    – juhist
    Jul 5, 2017 at 15:14
  • Fair enough. And since it could have been on the shelf longer than that, probably safer to go with another garage. Anyhow, feel free to downvote and/or flag for deletion.
    – anonymous2
    Jul 5, 2017 at 15:15
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While a battery may show low voltage if it's been sitting on a shelf for a while, when initially charged it should easily show 100%. If it doesn't... potentially a bad battery (or far too old). I would say that 11.9% might be nitpicking a bit... but the claim that a battery at 2% is still a functional battery is a bit of a stretch. While it may indeed be serviceable (ie, be able to be recharged and used), some damage to a 2% battery has almost definitely occurred (depending on the circumstances). After all, something had to drain that battery to 2%... and that something can't be good.

A new battery should be quick-charged by the shop to be 100% at the time of sale. Any less than that and it may not start your vehicle.

Note that I'm just a layman who just purchased a new starter, new battery, and a new battery tester... and I'm just going by what I read in the tester manual and seen on YouTube. But I believe this is fairly reliable. Something a bit trickier to research and understand is the SOC (state of charge)... having to do with how well the battery accepts a charge. My brand new battery is showing an SOC of 85% and won't go higher... and I've been told that definitely indicates a failing battery. Since it's brand new the store told me to return it for a free replacement and free installation.

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