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ex-jeeper
Member Since: 12 Feb 2011
Location: Cheshire UK
Posts: 34
 
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| Battery Volt Readings - Battery and/or Alternator Failing? |
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Having suffered a flat battery twice in the last week (Feb '08 HSE) thought it time to read up on the common issues. I have to say that this forum (and its knowledgeable posters) is superb!
Anyway, I am thinking that the 3.5 yrs old 90Ah battery is on its last legs, not sure about the alternator though. I have taken a few readings as below:
After flat battery was fully charged (took c.2 hrs to charge) Car driven c.40 miles with 3 engine starts in the afternoon. Car parked up and next day c.20 hours later (before starting car again) voltmeter across batt terminals gives reading of 12.02V.
Car then started and with engine at idle, reading across terminals was 13.75V.
After idling for c.5 mins, engine off, reading across terminals was 12.35V
I would really appreciate any input from some of you experts out there 
I am due to call back to the dealers with it soon and although they will check it out, would like to go pre-armed.
Cheers!
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 5th Jul 2011 8:15 pm |
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J@mes
Member Since: 10 Nov 2008
Location: Bomber County
Posts: 4547
  
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The only decent way to test a battery is with a DROP TESTER which puts a direct short circuit on the battery and measures the voltage while it is under a huge current load (the short circuit)
This tells you the voltage which can be supplied while the battery is in use, and is a proper indication to its condition.
It may measure 12v normally, but if it only measures 3v on a drop test then the battery is goosed.
Other way is with a dedicated battery tester, but they're expensive for DIY.
 2014 D4 XS
2005 D3 SE - Gone
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| 5th Jul 2011 8:21 pm |
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MrH
Member Since: 08 Aug 2007
Location: lost in the forest
Posts: 7754
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The at idle reading looks normal from a voltage point but it's Amps that count. Also, it takes about 9 miles to recover from a single engine start.
From what you've said, my gut feel would be that at 3.5years old, it's sounds more like your battery is starting to fail, but a proper battery (drop) test needs to be done. Also, a flat lead-calcium battery would take much longer than 2hrs to regain a full charge.
Hope that helps. LRs are a fond memory, apart from the maintenance.
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| 5th Jul 2011 8:25 pm |
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anglefire
Member Since: 09 Mar 2010
Location: In the Club House
Posts: 4180
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I had my alternator replaced last week.
Symptons were just about getting to 14.5V at normal crusing revs - idle dropped to 13-13.5 - turned on the heated screens and dropped to 11.5-12V barely increased with more revs.
(That was via diagnostics screen as some toe rag nicked my multi-meter 
From what you describe, battery sounds more likely. Mark.
2006, D3 SE Auto - gone but not forgotten.
2014 BMW 530d M Sport Tourer.
1977 Triumph Spitfire 1500
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| 5th Jul 2011 8:34 pm |
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Splitpin
Member Since: 30 Dec 2010
Location: At the toolbox
Posts: 535
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The best way to test a battery is with a amp clamp meter and a volt meter.
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| 5th Jul 2011 10:16 pm |
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Dunny1
Member Since: 18 Jun 2011
Location: Aberdeen
Posts: 116
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Hi guys i've got a 2007 HSE the battery was flat one day, charged the battery and the next day flat again jumped down to Halfords where the battery was tested and they said I needed a new battery cost £120. I asked them to check the alternator and it was pushing out 13.6 volts and was fine on their meter. I thought that was correct and acceptable, however a few days later battery finding it hard to turn over car spoke to a local LR guy I use and he said the altenator should shove out 15 Volts for the car and I needed a Alternator. There had been a modification to the D 3 altenators and it took me a while before I got one.
Apparently he had changed a few over the winter period.
regards Dunny1
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| 5th Jul 2011 10:28 pm |
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