Had recently replaced my battery in 80' 450sl (approx. 3 months ago) Car started fine, until recently, when hadn't used for approx 2 weeks. Went to start and wouldn't turn over. Jumped and started fine. Drove for approx 5 minutes. When went to start an hour later, needed to be jumped again. I know the battery was good when it went in. What could be causing this drain on the battery. Could it be the alterator or is it just that I needed to keep the car running for longer than 5 minutes to recharge.

Two weeks of sitting is certainly not enough to kill a battery, unless something is draining it, or unless something is simply wrong with the battery..

What is the resting voltage of the battery.. It should be about 12.4 volts or so at 70*F..A little less if it's colder..

You need to check for a bad connection at the battery..

If something did discharge the battery, 5 minutes would probably not be enough to re-charge it, which, BTW is very hard on your alternator..

Probably the best thing to do is take it out and have it properly tested..

If the alternator is not functioning properly, the light would likely be on.. That system works pretty well...

Jay

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89 300SEL Money Pit

92 Blown Buick Ultra Pimpmobile 220K and adding 1K per week

88 Wagoneer Slightly modified (Not for soccer moms)

04 Kia Sedona with every option... NICE

Excuse my mechanical ignorance (Industrial Engineer) by what/how would you check for bad connection at the battery??? Both cables look in great condition.

Well. Sometimes corrosion forms between the battery post, and the conector...You can loosen the connectors and pull then off, and look.. Clean them with a wire brush while you have them off..

What does the car do when you try to start it?? If it tries to turn over, but simply is too weak.. Then it's likely that the battery is discharged.. The question is why???

Without some voltage readings I'm just guessing..

Check the resting voltage of the battery.. If its at least 12V or better, try to start the car while testing the voltage.. If the voltage stays the same or approximately you have a bad connection.. If the voltage drops way down, and the car won't start the connection is fine..

Start the car via jumper cables.. Check the voltage after it has run for 5 minutes.. If it isn't above 13V it's likely that the charging system isn't working..

To check for something draining the battery, you'll need to disconnect the battery, and place an amp meter in line.. If you have more than a few miliamps of current then there is some device that is draining you battery...

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89 300SEL Money Pit

92 Blown Buick Ultra Pimpmobile 220K and adding 1K per week

88 Wagoneer Slightly modified (Not for soccer moms)

04 Kia Sedona with every option... NICE