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Mike, Mercedes Technician
Category: Mercedes
Satisfied Customers: 39198
Experience:  Tech Expert
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Just drove my sl(###) ###-#### first time in 2 weeks. Battery

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Just drove my sl(###) ###-####for the first time in 2 weeks. Battery light cone and says visit workshop, and the battery charge goes up to 8kw when driving and down to 0 when stopping, now my engine management light has just came on as well
Hello and Welcome..

My name is ***** ***** Im happy to help..

With this fault as you describe it, it sounds like the alternator( or its circuit ) has developed a fault... but - the battery itself should be checked first. This should be done by first fully charging the battery and then have it pro tested at a local garage. If the battery has suddenly failed, as they can do , that will cause what you have so that should be checked first.... a new battery would be the answer then.

If thats ok though - a proper test of the alternator output will find the fault. You should have circa 14.6 volts to the battery on a meter test... anything 12v or under or 14.8 / 9 or over, will be a charge circuit / alternator fault.

So thats the way to work through / get this sorted for you.

Of course - check the cabling /connections and alternator drive / belts first also.

Such erratic power -through / battery etc faults will cause the EML / engine light also - so once thats cured , likely as not, that will go off too.

If not - then a plug in diagnostic test would be required to check why thats on.

Let me know if you need anything else at all.. If you do get back to me, I will get back to you asap thereafter.

Meantime , please do now at this point, click on the "Excellent ratings" for me... I really appreciate that and Thank you....

Kind Rgds, MIKE..
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Customer: replied 3 years ago.
Thank you. The eml has now gone off. So it's either the battery or the alternator. I will get it checked tomorrow. It is driving ok. But will try battery first. Then your other suggestions thanks