Battery dead, but responded to a jump start

2005 SUBARU FORESTER
109,000 MILES
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DIANA FRITTS
  • MEMBER
  • 1 POST
Now inside dash lights extremely dim....could it be the battery or the alternator? Needed a jump start to get going this morning and engine ran fine (with 2 restarts after approximately 2 1/2 hours. Total of almost 200 miles. However, when I drove this evening, the interior lights were extremely dim...however, the engine seemed to run OK. Do I need a new battery or could it be the alternator or other cause?
Jan 10, 2012 at 3:55 AM
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CARADIODOC
  • ✓ASE Certified Mechanic
  • 34,321 POSTS
  • ASE Certified Mechanic
Start by measuring the battery voltage with the engine off and again with it running. A fully charged, good battery will read 12.6 volts. If you find 12.0 volts, it's good but discharged. Closer to 11 volts means the battery has a shorted cell and must be replaced.

With the engine running, the voltage must be between 13.75 and 14.75 volts. If it is low, and the battery is not shorted, suspect the generator.
Jan 10, 2012 at 4:04 AM
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