1st, I'm not a certified mechanic. If you follow my advice and blow your car up or die, call your mother. I take no responsibility.

Got this?


It might be a few things, but let's face it, when it comes to batteries, it's not if they'll go out, just when. So, if you have a 4, 5 + year old battery and you live somewhere where it gets very hold or cold, start by checking your batteries. I checked the one on the trunk with my multi-meter and it was putting out 12.7v without the motor running and 14.1v with the motor running. Good battery, good alternator. Now let's check what I suspected: the auxiliary battery under the hood (some are under the passenger seat):

Remove the dust cover using the 3 twist fasteners. Just twist them 180:


Now take out the cabin filter airbox. Just one 10mm nut and yank er' out:


Ah, there's the little sucker!


How's the voltage (engine off)? Not good! Should be 12v ish:


How's the voltage with the engine running? Should be 14v ish:


So, the alternator is putting out good voltage, but the battery voltage is low. It's not holding a charge, so she gots to go!

The newbie:


Charged out of the box too!


Old battery had threaded terminals (easy!) New battery uses bolts with threaded square washers. You can't insert them (threaded washers) once the terminal leads are in place, so I had to shim them in place outside of the battery tray, get a bite on the bolts and pull the shims out. Not a big deal though, just a bit more time/effort.


New battery is in!


The warning light still showed after I started the car. Crap! But, I let it run for a few minutes, turned it of, started it again and poof, error message gone! I guess the computer needs to read the voltage in spec for a few mintues before it will let the effor code go.

Total cost? $70.00. Dealer? I've seen others say they got soaked 400+ bucks!

Again, this error might NOT be your battery, but with a $30-40 mult-tool, you can easily check your batteries and alternator, both easy fixes if bad and the most common reasons for this error message.

Working on your car is fun and best off all, much cheaper!

http://www.batteriesplus.com/product...TAX14--BS.aspx

$65 with online coupon.

Or >>

Wow! That's a cheap battery. Hopefully it's good. The best deal I could find on an OE branded battery was $158.00 shipped. I'm sure it's good, but 2X as good? I don't think so.

I went w/ UPG AGM b/c I was familiar with them in the powersports industry as being a good battery for the money.

I must be missing something ? I see a battery light on etc but I don't get the leap to replacing the battery ? Sure its nice to know/see how it's done, but lets face it batter lights have been steering owners in the wrong direction of decades.

I didn't leap to replace the battery. I leaped to my multimeter and tested the batteries and charging system FIRST.

The aux. battery was putting out 7 something volts with the car off, but full charge with the car on. That means the alt is good, but the battery isn't holding it any longer. That's a bad battery.

Batteries don't last forever, the car is a 2006 and I know for a fact, neither of the factory batteries have been replaced. So not only was it highly likely a battery, testing before replacing anything proved it. My post was to show you how I solved MY problem.

You definitely are missing something. The battery light icon is even eerily similar to what a real battery looks like. Mercedes doesn't alert you the battery bad unless it really is. Other car manufacturers you are used to over the last few decades may have done this but not this model Mercedes.

That nice ! The way I was taught a battery with 10.5 volts or less is replace without any further testing. With a full cell missing theres no reason not to replace it. Seems to me a system like this could have been standard long ago. I own a 05 CL65 and am getting acquainted with its electrical and mechanical systems on the fly.