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E-Class, SLK
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Discussion Starter #1 (Edited)
I just noticed that the battery warning is illuminated at the right side of my 2001 SLK230 :frown. Does anyone know what is this about? Is there a problem with the recharging system or battery is going to be bad soon? Seems the battery is OK (2 years old) and, so far, the car is running fine. Thank you,

Update: It is related to the charging system (the battery is not being charged properly).
 

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99 SLK230 AMG Sport
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The first thing I would look at is the battery terminals. They can develop a corrosion barrier between the clamps and terminals. This causes the connection to degrade and the battery does not charge as it should. And the corrosion is there even though everything looks fine. This mimics a battery that is dying.
Just remove the clamps, scuff the insides with a wire brush or sandpaper, clean the terminals also. Reconnect and drive. Hopefully there's no charging problem.

Note: This is an incredibly common problem with cars here in Hawaii. Happened with my wife's car yesterday. The fix took five minutes and the car perked back up.
 

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Discussion Starter #3
Thanks Sharkboards, Cleaned both battery terminals and cables for better contact but the battery charge light is still illuminated on the dashboard. I also checked the voltage regulator and it's good. The car seems running OK but I don't want to take a chance. Does anyone know what are other components I should check out?
 

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99 SLK230 AMG Sport
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I would suggest testing the output voltage from the alternator while running. It should be charging at around 14 volts. If it's much lower, there is an alternator problem.

I suddenly recall the good old days when you could change brushes on a generator from the outside of the body, and without dismantling anything. Took about 10 minutes with just a screwdriver and a wrench.
 

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2002 SLK 230
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I would recommend running up to an AutoZone. They will bring their little tester out and check it for free...both the battery and alternator at once. I recently had to replace my alternator due to a failing voltage regulator. Cost around 150 bucks and the job is very easy to do yourself. If you end up going that route...Pelican parts has a guide, for the pre-facelift, but i used it with no issues as a guide on my 2002.

Pelican Technical Article - Mercedes SLK 230 - Name: Alternator Replacement
 

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Discussion Starter #6
Thank you Sharkboards and TehRage. The battery shows 12.2 volts (engine off) but it drops to 11.86 volts when the engine is running. This indicates the alternator does not produce enough juice to recharge the battery. A failing alternator can be related to a bad voltage regulator such as worn brushes or bad rectifier/transistor. Both brushes on my voltage regulator are almost gone. Since aftermarket v-regulator is cheap ($18.89 USD) I just ordered one to try it first before replace with a new alternator.
 
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