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Old 05-16-2008, 02:43 PM   #2
Mulder
Trust no one
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Member#: 11170
Join Date: Oct 2001
Chapter/Region: Tri-State
Location: NYC
Vehicle:
02 WRX
15 WRX/05 GTO

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The battery may have one or more weak cells, if it's the original battery it's well past its typical life expectancy. Many of them have crapped out much earlier.
If you have a battery hydrometer (looks like an eyedropper with balls in it, about $5 at parts stores) you can check the state of charge in each individual cell to see if there are any bad ones. If any cells use more water than the rest that's a good sign they are bad.
Also most parts places will test the battery for you, or if you know a local shop they may do so.
I would not be at all surprised if your battery is shot.
Your voltage reading with the engine running is normal so most likely your alternator is ok, although it is possible to have some bad diodes (which will reduce charging output) and still see normal voltage with a meter. This type of problem can be diagnosed with a scope at most well-equipped shops.
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