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I bought an 1982 240d three years ago. I love it. I'm wondering about the battery. Is there any warning when it's about to die? Can I test it in any way? Thanks. Herb
 

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1959 220S cabriolet, 1983 240D original owner, 1999 E300 turbo diesel, 1988 560SL, 2003 SLK320
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Most McParts stores will test it for you for free, but the way batteries are manufactured now, they often times will give no warning when they are going to fail on you. Some people will just replace them when they reach five years to be safe, figuring that they have served their useful life. Others will wait until they die and call Mercedes Roadside Assistance and let them replace it. For a replacement battery, the Optima is spoken of highly and I've had good luck with the Interstate MTP-93.

Len
'83 240D 344,000 miles original owner
 

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Batteries are tested ( even today[:)]) by measuring their standing voltage - at rest not having been charged or starting a car in the last ten minutes. They should read about 13.75 volts.

They are then discharged at a consistent rapid pace for 5 to 10 minutes. They ending voltage is measured. If in that short time it drops below 12.25 volts it's considered on its last legs. A good parts store or auto battery store can do this test - but realize a lot of them are anxious to sell you something.

The typical lead-calcium flooded cell ( your typical starting type battery) signals it's near the end of life by bouncing back slowly and not hitting the old peaks. It will crank the car a little more slowly and in stop and go trips and will seem to not come back up to charge fast enough.

The Optima is an excellent battery. It is a sealed spiral cell battery with very low amounts of acid in a mat wrapped between the plates. It can give a lot of power for its size and can have a long life. A couple things - they are very expensive for what they give you and they are very sensitive to overcharging. They can lose their very small amount of electrolyte through a pressure valve if the voltage isn't carefully controlled. Most Mercedes with microprocessor based voltage management systems should be OK ( if you don't mind the $$$) but the older relay based systems - such as a 240D may not be up to the task.[xx(] Your typical DieHard or Interstate batteries are much better at this - and at 1/3 the price.

Check yor local Interstate distributor. They commonly sell seconds and blem's for $30 or so. It's an incredible deal on a very good battery. They can't sell first runs because that conflicts with their retail shops but do you really care if the label on a battery is a little crooked? If that's not practical your best deals are a Sears sale on DieHards,or WalMart, PepBoys or Costco...

Buy all the AmpHour and Cold Cranking Capacity you can properly fit in the holder.

Good luck
 

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Discussion Starter #4
Thank you, Mike. I didn't unerstand everythingthat you wrote but it will help me when I look to replace the battery. Herb
 

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Thank you, Len. I hope to reach the number of miles that you have if the rust doesn't get the car first. I've had some quotes on cutting out the rusty parts but they ask more than the car is worth. Herb
 
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