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Adding distilled water to my car battery, I've noticed only the side cells very short of reaching the meniscus.

The most positive cell, facing the front of my '08 Jetta 2.5L (which has empty space, and probably collects a lot of heat from the engine, especially when the two frontal engine cooling fans are on), required almost 90ml of water, the next cell only some 50ml, the following ones seem to already be at around meniscus (added 20ml each for prophylactics after 6 years of service), and final negative one, closer to the cabin, 40ml.

Is it always like this? If so, why aren't they making cells of varying size and level of meniscus, so that more water could be contained within the cells more likely to be kept at a higher temperature and evaporate and/or gas prematurely?

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    In these days of cost conciousness it is usually a case of simply replacing an aged battery (3+ years) if it presents a problem. – Allan Osborne Dec 9 '14 at 21:15
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    When you buy a battery it will come with a warranty, usually three years. This is its life. Lasts longer its a bonus. Having changed thousands of batteries over the years I can only think of your assertion that 'most batteries are changed pre-maturely' is based on supposition and conjecture rather then any real monitoring of battery replacements. If it makes you feel any better, I have just replaced my cars battery for £71. Winter has arrived in the UK. – Allan Osborne Dec 9 '14 at 21:36
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    @AllanOsborne, don't cars themselves come with a 3-year warranty? Are you giving your 3-year-old cars away, too? The fact that batteries are replaced prematurely is a widely known fact -- batteryuniversity.com/learn/article/… -- "A leading Germany battery maker checked 400 starter batteries that had been returned under warranty and found that 200 of them had no problem. Additionally, prior to replacement, do you actually bother to check water level, and put the battery on the charger overnight? Or, who has the time, right? – cnst Dec 9 '14 at 21:44
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    Your 'battery university' is a company that makes battery testers so it not subjective nor independant in the 400 batteries story. As for a three year old car out of warranty repairs, if the owner does not pay to have a repair then they might as well give the car away as it will simply become a lump of immovable steel. The warranty being for three years means just that. Charging a battery overnight to see if it will revive just does not happen any more with the advent of conductive testers, say Midtronics. – Allan Osborne Dec 9 '14 at 22:01
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    @AllanOsborne My battery is an Odyssey battery. It comes with a 2 year warranty and is the most expensive battery. I have an Odyssey battery in a motorcycle and it has been working great for the last 12 years. I have used their batteries in many vehicles and they usually outlast the vehicle. I'm glad I don't follow your advice. – Paul Dec 10 '14 at 8:30
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In a word, no. Any of the cells might need water. All of them would need water (or electrolyte) if it were tipped over. Usually when one needs it they all need it, but no rhyme or reason to it.

  • It is completely normal for wet flooded cell batteries to require more frequent refills when exposed to heat, even on a cell by cell basis. It's just more rapid evaporation. – Paul Dec 10 '14 at 8:37
  • @Paul ... If anything, the inner cells will get warmer due to charging and not having the ability to dissipate heat because of lack of surface area (only the two end cells have more). The inner cells would suffer worse than the outer cells. I would expect, if anything, the inner cells would have more evaporation than the outer. – Pᴀᴜʟsᴛᴇʀ2 Dec 10 '14 at 11:48
  • Heat generated by normal charging is minimal compared with heat generated by the engine, which is the problem described in the question. – Paul Dec 10 '14 at 15:30
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Battery manufacturers make batteries to international standards, one of which was selected by VW as the battery for your vehicle. The problem you describe is specific to your vehicle, so a battery manufacturer would not be able to solve the problem as you are suggesting without violating the standard or creating a problem for the owner of some other vehicle that uses the same battery type.

The solution that battery manufacturers have come up with for the problem you describe is a maintenance free battery.

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    Maintenance free batteries have an excess of electrolyte and most have a pressure valve arrangement to minimise electrolyte loss when charging/gassing. This is intended so that the battery will be trouble free for its designated life/warranty. – Allan Osborne Dec 10 '14 at 10:41
  • @AllanOsborne It does not matter how the manufacturers arrived at the solution of maintenance free, just that they arrived at it. Note that VLRA batteries are not maintenance free because of the reason you state. – Paul Dec 10 '14 at 15:31
  • Maintenance free batteries are not maintenance free is literally what you are saying. How about, A maintenance free battery that requires maintenance during its service life is a faulty maintenance free battery, or it is the wrong battery for its implementation. – Allan Osborne Dec 11 '14 at 11:11
  • @AllanOsborne I have no idea how you come to that conclusion. I have owned a great many maintenance free batteries and not one has required maintenance, and I've never heard anyone ever say that maintenance free batteries are not maintenance free, until now. – Paul Dec 12 '14 at 23:16
  • My battery IS maintenance free. Maintenance free batteries, sadly, still require for the water to be added. – cnst Feb 16 '15 at 18:36

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