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Old Aug 22, 2008 | 07:12 PM
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Battery Test Question

I searched but didn't find anything specific to my problem...

The voltage readout on my scangaugeII is now reading 12.8 to 13.2 while driving. Used to be 14.0 to 14.2 a few months ago. The batteries are the originals so I am thinking it's time for new ones (4 years and 54k miles in Vegas heat). Okay...the question.

The guy that tested them at Autozone didn't disconnect them from each other while testing. Don't you need to test each one separately? He said they were still good.

Any suggestions on the type of batteries? I know the optimas are the best but they are out of my price range.

Thanks for the help!
 
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Old Aug 22, 2008 | 07:21 PM
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I don't think you have to disconnect them to test them but hook a multimeter to them well the trucks running if its below 12v they are not charging. Replace them soon before it burns up your alternator they arn't cheap. Make sure you replace both of them not just one.

I use interstates I've only had them for a year though. They weren't the cheapest, but batteries is one thing I don't think you should cheap out on.

http://www.interstatebatteries.com/e...%7C%7CRank%7C1
 
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Old Aug 22, 2008 | 10:28 PM
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Thanks for the reply. Right now they are at 12.8 to 13.2 while running. Just a few months ago they were at 14 so I think it's time to get new batteries.
 
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Old Aug 22, 2008 | 10:41 PM
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Umm, that tells me you have an alternator failure, not a battery failure. I'd borrow a battery from a friends truck. It should still start and run with just 1 battery. If your voltage is still low with a friends battery, then your alternator is blown
 
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Old Aug 22, 2008 | 11:31 PM
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Well, that would suck. The batteries need to be replaced anyway. 4 years in Las Vegas heat is enough. I might be driving to Alaska this fall anyway and I will want new batteries for that. So...I will get the new batteries then see what it looks like. If it is still low while running with the new batteries then I guess it will have to be a new alt as well! JOY.
 
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Old Aug 23, 2008 | 11:13 AM
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Autozone checked my batteries the same way and said that they were good. Three days later the truck would not start. Replaced both batteries with duramaxes from Autozone and no more problems. Just completed a trip to the Sierras for 10 days and got 11.6 mpg going and 13.3 mpg returning pulling a 12k 5th wheel.
 
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Old Aug 23, 2008 | 12:45 PM
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If you're replacing your batteries, have your alternator tested as well. If you've got a dead alternator, you'll be replacing those batteries again real soon.
 
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Old Aug 23, 2008 | 12:55 PM
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Once the new batteries are in if your charge voltage returns to 13.5 to 14.2 volts then you should be good to go. Usually!
 
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Old Aug 23, 2008 | 01:28 PM
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IMO - buying your own load tester is almost a necessity when you have two expensive batteries.

It probably is one of the more frequently used troubleshooting tools you can have.
 
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Old Aug 23, 2008 | 05:52 PM
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Replaced my batteries this morning. The voltage is now at 13.0-13.3 while driving with AC, lights and radio on. It is the same when everything is off. When starting it drops to 10.

That seems okay. What do you guys think?
 
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Old Aug 23, 2008 | 06:00 PM
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Mine drops to 12.8 right after starting, even in the cold, returns to 13.1 or 13.2 volts shortly after and stays at that. I think you are fine.
 
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Old Aug 23, 2008 | 07:18 PM
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They must be lowering the voltages. Most vehicles I've seen have a running voltage of 14.2-14.4.

EDIT: I thought 13 sounded low. Just looked it up, the "float" charge (not fully charged, but you can keep it hooked to this voltage for ever with out major problem, but battery life will be reduced), should be about 13.6-13.8 volts. The full top off charge voltage is 14.4.

So while you won't have any problems with those voltages, your battery life will be reduced.
 
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Old Aug 23, 2008 | 09:50 PM
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Originally Posted by Lead Head
They must be lowering the voltages. Most vehicles I've seen have a running voltage of 14.2-14.4.

EDIT: I thought 13 sounded low. Just looked it up, the "float" charge (not fully charged, but you can keep it hooked to this voltage for ever with out major problem, but battery life will be reduced), should be about 13.6-13.8 volts. The full top off charge voltage is 14.4.

So while you won't have any problems with those voltages, your battery life will be reduced.
Where did you look this info up? Sounds like a great resource. Thanks for the info.
 
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Old Aug 23, 2008 | 10:48 PM
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Well wikipedia.org , which isn't the more reliable place. But many other websites also say the same thing about Lead-Acid batteries (what cars and truck use)
 
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Old Aug 24, 2008 | 09:22 AM
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Batteries should be LOAD tested seperately. But with that said, 4 years on batteries is way to long. If you test both batteries connected together, one could be masking the other. Always test serperately.
 
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