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I was discussing where to buy car batteries with a friend who is a professional driver and who has briefly worked as a mechanic. He suggested buying from one particular shop for several reasons, one of which was that they have a high turnover of stock and that therefore the batteries haven't been standing as long on the shelves. The shop I'd been thinking of going to, he recommended against because selling car batteries is only a small part of their business and he expected the car batteries to be in less than ideal condition from having been in storage for a very long time (years, potentially).

Does this reasoning make sense? I thought car batteries only degraded and discharged when left connected for long periods, and so leaving them boxed and unconnected would not be a problem.


A few clarifcations:

  • These are all the "maintainence-free" sealed type of lead-acid battery
  • It's worth mentioning that this is Sierra Leone, West Africa, and most car batteries on sale are Chinese or Nigerian brands that are not on sale in Western countries. There might be minimum standards or regulations which would be taken for granted in some countries that aren't necessarily met here (my local friend is always very negative about their quality and jumps at the chance to buy batteries imported from countries with stricter regulations)
  • Temperatures vary from about 15°C to 40°C, and they don't appear to have been stored in any particular special way
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    I have also heard such rumors, the reasoning would be that batteries naturally lose charge even when disconnected, and storing partially discharged batteries greatly reduces their lifetime. Therefore it's a good idea to buy from places where batteries come and go quick or at least decode the manufacturing date from the serial number. Though I've also heard, that shops selling batteries are (should be) charging them once in a while to retain charge. Looking forward to the answers. – I have no idea what I'm doing Jan 21 '16 at 11:45
  • They usually have a manufactured date stamp on them, so it wouldn't be difficult to check how old it is before paying. – HandyHowie Jan 21 '16 at 12:49
  • @HandyHowie Definitely depends on the manufacturer. More often than not I found it to be coded within the serial number instead of being written clearly. – I have no idea what I'm doing Jan 21 '16 at 13:09
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All batteries have a self discharge rate. This comes form the inherent nature of their chemistry. Lead acid batteries are one of the worst offenders when it comes to their self discharge rate. The estimates are all different but between 5% and 20% of capacity discharge a month is the general consensus. Because the discharge rate is a function of current capacity the discharge is a decaying exponential. The battery will go flat eventually but the less charged it is the slower the rate of discharge is.

Allowing the battery to discharge while in storage is not inherently bad. What is bad is allowing a lead acid battery to go totally flat, ie 0V. This is where the damage comes from. If the battery didn't go below roughly 9v I would not be concerned about its health.

  • Honestly, I've never seen a car battery that is at 0V. 9V already means it's way dead. – I have no idea what I'm doing Jan 21 '16 at 15:37
  • @IhavenoideawhatI'mdoing Don't get me wrong, at 9V the battery needs recharged but is not damaged yet. – vini_i Jan 21 '16 at 16:13

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