Two months ago our MkV Golf was given a major service by a VW dealer and the battery got a good bill of health (tick in the green column).

This morning it failed to start and after an hour or so top-up from a charger, taking it to Kwik-fit got it diagnosed as having a measured battery EN(A) of 281 vs a rated value of 570. They suggested a replacement...

Could it have degenerated that far in a couple of months? It was the original battery on an '08 plate.

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    Only if they tested the battery which is not common to do during most service routines, I would call the dealer that did the service and complain about ti, see if they offer anything for your trouble. – Moab Aug 3 '16 at 17:58
  • They did but it's only a red, amber, green-type thing. Would it really have gone from green to knackered in two months? – lane Aug 3 '16 at 18:44
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    The green indicator only reads one cell of the 6 in the battery and is not reliable for overall battery health, only a proper test of the battery is reliable. ie: electronic tester connected to the battery or a battery hydrometer to test each cell, if the battery has cell caps that can be removed. – Moab Aug 3 '16 at 20:11
  • Depending on your latitude and usage, modern car batteries may last only 3-4 years. They're a consumable item. Its not impossible that your battery was original, but its unlikely. – Criggie Aug 3 '16 at 20:23
  • I had a battery go 11 years, took it back to AutoZone for a warranty, they laughed so hard. – Moab Aug 3 '16 at 20:45

It isn't unusual to see that an ageing battery works fine one day but fails to start the engine the next day; it's normal for a battery to discharge over time, even when it isn't subjected to electrical loads.

From the Bosch Automotive Handbook:

Modern batteries using the lead-antimony alloy lose approximately 4-8 % of their charge every month when new. As [the] battery ages, this value can increase by up to 1 % or more each day due to the migration of antimony to the negative plate and other impurities, until a point is reached when the battery finally stops functioning.

  • Damn - so no credit due from the dealer... Ho hum - thanks for the info! – lane Aug 3 '16 at 19:36
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    Modern batteries are lead-calcium, not lead-antimony. – Paul Aug 3 '16 at 20:24
  • @Paul I'm not a chemist, would that change the mode of failure? – Zaid Aug 3 '16 at 20:46
  • One of the biggest advantages to lead-calcium is the reduced self-discharge rate. I'm not sure if this impacts any changes to the self-discharge rate over the service life of the battery. – Paul Aug 3 '16 at 20:49
  • @Paul it could be that they mentioned lead-antimony because they had hard data for it. I don't think they're implying that all modern batteries are lead-antimony – Zaid Aug 3 '16 at 20:55

A MkV Golf would have had its warranty run out, so the dealer is not going to perform the entire scheduled maintenance/inspection/certification as they would for a car under warranty or going to be resold by them. This would include:

  1. Visual check of the battery (is it leaking? cracked?)
  2. Check the "magic eye" - the indicator (green, black, yellow) of battery health

Only if they saw something obviously wrong (corrosion all over, leaks), non-green in the magic eye they would continue with an actual load test. The service technician is going to mark the battery as good as he started up the car, heard it started normally without slowness, didn't see any voltage light on the dash, and the above 2 things checked out.

Your battery was nearing 8 years old if the car was sold in 2008. The lifetime of a battery is generally expected to be 4-5 years. Cold weather, rough conditions, not keeping it charged and low water will all contribute to less battery life.

  • The sheet that came back from the service listed "Check battery condition with test machine". Is this not standard for a major service? – lane Aug 3 '16 at 19:34
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    @lane you can't prove that they didn't test it, and that it passed the test. In any case, a typical hand-held battery tester doesn't give you much more information than observing that the cold engine cranks normally - unless the engine won't crank and you want to check if the problem is the battery or something else. In about 40 years of driving, I've never had a battery failure with more than about 24 hours of warning - and usually there is no warning at all. – alephzero Aug 3 '16 at 21:30
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    @lane Well, if it says "Check battery condition with test machine" then they either did not do it, or the battery deteriorated rapidly. Both very likely. You have no recourse to the dealer regardless - you need a new battery. – mikegreen Aug 3 '16 at 23:42
  • Do batteries still have a visual indicator ("magic eye")? I haven't seen one of those in many years. – TMN Aug 4 '16 at 12:56

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