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Old Jan 7, 2014 | 10:00 AM
  #1  
brandon.edwards's Avatar
brandon.edwards
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Batteries

What should voltage be on my batteries when they have sat overnight, and i come out to start it up? What is normal operating voltage after it has warmed up?

When i go and start my truck usually after ive let it sit at work after my 12 hr shift, it start/cranks slow and always fires right up, but the voltage lags around 11.1- 11.2 and the battery light comes on. After a couple seconds go by the battery light goes out, the voltage jumps to 13.2- 13.9 and the idle goes to normal. I thought i may have had weak batteries, but went in to get em tested today, and they both checked out great.
Any thoughts?
 
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Old Jan 7, 2014 | 11:22 AM
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May have both weak batteries and a weak alternator.

You should see around 12.6-12.8 volts at the battery @ 70 degrees. The colder it is the voltage drops. It wouldn't be uncommon to see 12.3-12.4 @ 32 degrees.
 
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Old Jan 7, 2014 | 12:44 PM
  #3  
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And if you decide to replace them ALWAYS change them as a set.
NEVER replace just one!!
 
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Old Jan 7, 2014 | 08:25 PM
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I have new Motorcraft's; when I fire up my volts jump around from 11.6-12.0 ... after a few secs (assuming after GP's turn off), they jump to 13.5+.
 
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Old Jan 7, 2014 | 08:34 PM
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Originally Posted by brandon.edwards
What should voltage be on my batteries when they have sat overnight, and i come out to start it up? What is normal operating voltage after it has warmed up?

When i go and start my truck usually after ive let it sit at work after my 12 hr shift, it start/cranks slow and always fires right up, but the voltage lags around 11.1- 11.2 and the battery light comes on. After a couple seconds go by the battery light goes out, the voltage jumps to 13.2- 13.9 and the idle goes to normal. I thought i may have had weak batteries, but went in to get em tested today, and they both checked out great.
Any thoughts?
your alternator is not charging your batteries past about 25% charge.

you need an alternator that outputs 14.5~14.8 volts. the OEM will never
do that. ever.
 
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