While I would not think a six month old battery is likely to be bad, I would not rule it out simply because it is only six months old. Don't asssume anything. Check it. I've had three month old batteries that were bad! I'm sure others here on the forum have had the same experience. This has happened to me twice over thirty-some years. I think it unlikely that it is bad, but check the battery, and check everything else. The battery could be bad because the alternator or regulator is bad.

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Mike

2000 SL500 22,000 miles
1981 300CD 188,000 miles
1979 450 SEL 266,000 miles
2005 Cadillac CTS 25,000 miles