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manichauhan
Member Since: 24 Oct 2010
Location: London
Posts: 56
 
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| Unusual 2v voltage drop on battery |
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Hello,
An unusual problem has just developed on my discovery 3 (2006).
After the ignition is turned off, there is a 2v voltage drop on the battery after about 30 seconds.
While the car is running, the voltage is about 14.5V. This indicates the alternate is ok. When it is switched off, the battery voltage slowly trickles down to about 12.67v (which I believe is normal) and then suddenly drops about 2v down to 10.4 v and then stays there without any further battery drain.
Due to the now low voltage on the battery, the car struggles to start again (with the usual fault messages associated with low voltage etc). When it does start up, the voltage returns to 14.5v.
I have checked the battery and verified that it is holding charge, so it appears there is some sort minor drain after the ignition is turned off.
The car has been working fine recently until now. The only recent changes were
1) replacing the front suspension lower rear bush
2) replacing the standard side marker bulbs (the outermost small bulb in the headlamp) with LED ones.
The problem started occurring a short while after 2) , so I suspect it may be linked to that. I have changed the bulbs back to the standard ones, but the problems continues to occur, so it's maybe just a red herring.
I don't know much about what happens after the car ignition is turned off, so any advise or pointers would be most appreciated.
Thanks
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 15th Jun 2015 8:46 am |
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Bodsy
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Member Since: 06 Nov 2006
Location: In the Clubhouse
Posts: 21361
 
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Just sounds like a fubared battery losing a cell Bodsys Brake Bible
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| 15th Jun 2015 9:56 am |
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CUCO
Member Since: 27 May 2011
Location: Spain & Oleee!!!
Posts: 609
  
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Yes...  bad cell
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| 15th Jun 2015 9:57 am |
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manichauhan
Member Since: 24 Oct 2010
Location: London
Posts: 56
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Thanks Bodsy, Cuco,
That's what I thought too, but I then removed the battery, trickled charged it fully and tested it with a multimeter every 30 minutes. It didn't lose any charge at all.
REconnected the battery again and same symptoms as described intially.
Would a bad/failing battery cell behave like this ?
Thanks again
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| 15th Jun 2015 11:26 am |
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lynalldiscovery
Member Since: 22 Dec 2009
Location: Maidstone
Posts: 7274
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Easy way to check battery is after it has stood for several hours overnight is best, then check the voltage, not very scientific but gives you a good idea whats going on.
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| 15th Jun 2015 11:48 am |
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CarlW
Member Since: 07 Aug 2005
Location: Lancashire
Posts: 111
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Long shot but try checking for a drain at both ends of the battery when it's in the vehicle.
Many years ago I had a car with a similar battery problem and I found a drain at the negative end of the battery but not the positive end - it turned out that a sharp metal object had embedded in/punctured the bottom case of the battery and made contact with the metal plates inside and was shorting one cell when the battery was in the metal batty tray but there was no acid leaking out. A similar problem would explain why the batty voltage stays up after you've charged it outside the vehicle. Disco 4 Landmark
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| 15th Jun 2015 9:03 pm |
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manichauhan
Member Since: 24 Oct 2010
Location: London
Posts: 56
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Thanks all for the replies.
After the pointer to the bad cell possibility, I did some research on the internet and found the following:
**********************
A healthy 12 volt battery should maintain a range from 9.5 - 10.5 volts under the load for a good 30 seconds straight. If the battery begins to hold and then steadily drops in voltage, there is a problem. If the voltage instantly drops to 0 volts, that is also a problem. We call this the open cell. On a new battery, this can be a result of manufacturing flaws, but it also may be caused by sulfate crystal buildup. Under the intense heat of the load, one or more of the weld pieces connecting the cells is coming loose and separating. This will cut the current, and voltage will drop. When the battery cools off, the pieces will touch, barely giving a complete connection. This gives you a false voltage reading. Batteries with open cells may read fully charged in idle, but they fail under a load test every time. Once a battery reaches this point, there is no going back. The best thing to do is recycle the thing.
*********************
This explains why the the battery didn't lose charge when it was off the car. To verify, I was going to test the battery off the car with a resistance load to see if the symptoms still occurred, but I think it's pretty much a no-brainer that it's the battery. Will be ordering one tomorrow. Thanks again
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| 15th Jun 2015 9:17 pm |
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CDS
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Member Since: 12 Oct 2009
Location: All over the UK!
Posts: 3331
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DSL wrote:https://www.tayna.co.uk/EA1000-Exide-Premium-Car-Battery-017TE-P7488.html
Might be a little bit off with D2BOYS code.
Good buy these babies Del
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| 16th Jun 2015 12:09 am |
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drivesafe
Member Since: 23 Feb 2006
Location: Gold Coast, Australia
Posts: 867
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manichauhan wrote:A healthy 12 volt battery should maintain a range from 9.5 - 10.5 volts under the load for a good 30 seconds straight.
Hi manichauhan, the info in that quote is what you should expect to see if you apply a load equivalent to the sort of load that starting a motor will cause ( a few hundred amps ) and is related to the CCA of the battery.
If your battery has dropped a cell, with a small current load, like what a compressor fridge ( around 5 amps max ) will apply to a battery, will cause the voltage to drop to 10.5v and then stays at 10.5v. Any similar load will do the same. 2008 TDV8 RR Lux + 2009 D4 2.7
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| 16th Jun 2015 8:56 pm |
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