Did I get yet another dub Mercedes Battery? Or at least a not so good one.If

Submariner1

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CL500 2009 5.5
firstly the car starts first time etc. So no crucial issue, but having installed a dash cam and I want to put on a rear dash cam ... every little bit of charge could be useful in Parking mode.

Some may remember my previous battery saga. Basically changed a perfectly good working battery purely as it was 7.5 years old, as I do low mileage.
Only to get a defective one! Sent the car haywire! Car failed to start the next day.
Mercedes replaced it and all the fault codes disappeared. They spent 5 hours checking it out ... so no car issues.

The cars parasitic drain fluctuates between 30mA and 20mA, with occaisional spikes for say 30 seconds to a few minutes of 40 or 50mA.
Mobilo guy says that fine, if not good, and very often he sees cars where it is up to 60mA.
They are basically only concerned if it goes above 60mA.

However I have noticed this replacement Battery (manufactured 2 weeks before delivery and showing 12.8V uninstalled) doesnt seem to me to be a “good un”.
Or is it the fact that it's cold weather.

( Note numerous web sites conflict some say cold weather decreases measure voltage others say it increases ) the disagreement seems to be about 50/50.

When I got the car in a warm september the original battery could often show 12.5V or 12.6V.
In comparison my new SL500s, generally would show 12.7 or even 12.8V.
Admittedly then I was unaware of Sam and control modules shutting down issue and the effect on measured voltage.

I know all that now!, all consumers off, incl ac and command, doors and boot shut and locked! And specifically the bonnet catches pressed down! Only then will the car fully shut down quickly; and it then does it in 1 or 2 mins.
Ignore any of the above, and this baby can take 30 to 40 mins to fully shut down.

Current situation:
If the car has not been run for 2 or 3 days, if I measured the voltage very quickly, it can occaisionally show 12.1V or 12.2V. As the modules shut down it will rise to 12.4V. Or even 12.5V
To me thats not really enough? For a new periodically charged battery.
I would expect 12.6V or ideally 12.7V.

If I charge it on the best new CTEK charger, specifically designed for AGM batteries - max 3.6A and 14.9V (CTEK Start Stop) with no AGM killer “15.3V Desulphation cycle” for say 8 hours ... it goes into low voltage Care mode. The Final on charge figure is 14.8V with a charge current of 0.24A. It then drops down to 13.8V in Care mode .

All OK.
If I wait over night for the residual charge to peter out, it shows 12.6V ... imo not too bad, but not great either.
Drive it for 10 miles , and thrn leave it 2 hours, and after the car shuts down, it shows 12.7V (not bad :)).
However Leave it 2 days, and its dropped back down to 12.4V or 12.5V ... a little low???

However, If you charge it for say 7 hours to get it to go into “Care mode” at 13.8v with 0.24A current, and then continue to leave it on charge over-night, that really takes it to its max charge level. Disconnected It Shows 13.2V, which drops quickly and the following day you will see 12.8V .. that seems pretty good.
But leave it uncharged or driven for 2 more days
And its back to 12.4V

Question is under those circumstances is 12.4V good / normal / bad? Bearing in mind its quite cold?

My observation is when we had the warm spell circa 9C it seemed to read a little higher say 12.6 or 12.7V. Is that normal?

I guess my real concern is, say its not been charged or used for 2 or 3 days to find it only measures 12.1V or 12.2V as it is shutting down the modules is imo pretty concerning.
Just carrying that small load to shut down really lowers the voltage ... imo that looks like signs of a weak battery. But is it?

I would like to know now, as its easier to get a replacement battery, when its only a few months old. Rather than wait 18 months and then bitch.

However I suspect, MB may say, well it shows 12.4V and thats within spec. So get lost. And then when its 23 months old , you betcha it will keel over and die!


Apologies for the lengthof post, but without an understanding of all the facts; it would be difficult for someone to comment constructively.

And finally due to the conflicting info on the web
Is it correct that as the temperature drops, the voltage of these batteries will drop too?.
Some say it increases! [ note I am not talking about the recommended charging voltage relative to ambient temperature , but the voltage one would see on a multimeter ]

Obvious recognised flaws in my findings:
1.Current drain measurement was taken by a Fluke clamp meter so not as accurate as in series multimeter.
2.these readings are “on the car” so not nearly so accurate, as say measuring the battery when its disconnected.
 
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Paul Goff

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2002 C220CDi CD Estate
If you take the battery to the supplier with a view to getting it replaced, they should test it to determine whether there is a fault or not. As most modern batteries tend to go on & on & on & on, and then roll over very suddenly with a dead cell, given what your readings are, I would say that your battery will pass the suppliers test and they will smile sweetly and hand it back.

The definitive answer re ambient temperatures and battery voltage is this,
As the ambient goes down, the battery voltage will go down, but only slightly.

My considered opinion is that your battery is fine, and even if it does inhabit the lower end of the manufacturers specifications in some way, if you keep it on your Ctek, you have absolutely nothing to worry about.
 
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Submariner1

Submariner1

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If you take the battery to the supplier with a view to getting it replaced, they should test it to determine whether there is a fault or not. As most modern batteries tend to go on & on & on & on, and then roll over very suddenly with a dead cell, given what your readings are, I would say that your battery will pass the suppliers test and they will smile sweetly and hand it back.

The definitive answer re ambient temperatures and battery voltage is this,
As the ambient goes down, the battery voltage will go down, but only slightly.

My considered opinion is that your battery is fine, and even if it does inhabit the lower end of the manufacturers specifications in some way, if you keep it on your Ctek, you have absolutely nothing to worry about.

Thanks
Pretty much sums up what I thought.
Its within spec ATM, and wouldnt be replaced.
But not good news for me as a low mileage user.

Thankfully I have Mobilo Breakdown, which covers this battery so its their risk not mine :)
 

Flyinspanner

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CLK320-A209 (sold CL500 & W168)
From the thread title I thought you must have had an “Ever-Reggae” battery :)
 
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