Battery Replacement

[survey]

My C 207 uses a Varta 80ah AGM battery. Found it on Ebay. After charging right up the present battery settles at 12.41v. I guess this means it's on its way out after 9 years and 73k miles?

Looking at the handbook ( that doesn't even list the battery spec) it states that after installing new battery one has to reset the clock and also the function for folding the exterior mirrors. The latter appears to only be by folding the mirrors out once. So is that all that will be disturbed? What about memory seats etc? Or should I get someone who can temporarily connect the positive and negative leads so there is no loss of continuous connection?

Anything that I should be aware of?

 

[Gazwould]

12.41 V , I wish , mine settles at 12.0 V
10.5 years old .



Starts with good cranking speed .

 

[survey]

12.41 V , I wish , mine settles at 12.0 V
10.5 years old .

View attachment 117846

Starts with good cranking speed .

Really? Mine starts OK at its 12.4v. It has not had many decent runs so maybe it's just dropped because of this. Maybe I need to just monitor it and keep it charged every so often. I always thought 12.4 was about a cut off from good to deadish.

 

[Gazwould]

A battery tester says replace and I will when cranking slows , possibly this winter , who knows .



Peeps are replacing expensive AGM batteries well before us , good old Stop Strain and over sensitive modern car electrics .

 

[mioba]

MB genuine are top batteries, cant go wrong with the longevity, get another and be done with it for ten years.

 

[survey]

So what problems with the car's electrical functions will there be by disconnecting and replacing the battery? Really need to know if its a DIY job.

 

[Gazwould]

So must Varta and Bosch .

All three made in the same factory !

 

[E55BOF]

MB genuine are top batteries, cant go wrong with the longevity, get another and be done with it for ten years.

Made by Varta or Bosch.

So what problems with the car's electrical functions will there be by disconnecting and replacing the battery? Really need to know if its a DIY job.

Probably none, but to be sure connect a trickle charger to the charging points under the bonnet while you change the battery. That maintains voltage in the system for where it's needed (if it is).

 

[survey]

Ah, hadn't thought of applying a charger to the positive and negative posts whilst removing the battery terminals and taking battery out. I assumed those posts connected to the battery and wouldn't accept a charge without the battery being present.

 

[E55BOF]

They do connect to the battery, but unless you detach the other leads from the main positive terminal that actually connects to the battery, the charger will maintain power to the rest of the car as well.

 

[survey]

My garage advised being careful with varta batteries that seem the same as the mb originals. In their experience they are not as good as the mb varta ones!

 

[E55BOF]

I rather doubt it. Varta are a very well-respected name in batteries.

 

[survey]

I rather doubt it. Varta are a very well-respected name in batteries.

That was my thought. Will get a drop test on mine as my garage said MB battery will last at least 10 years. They reckon probably due to non regular use. However charged right up 2 days ago and overnight dropped to 12.4. Trip out yesterday for only 12 miles. Overnight dropped to 12.3.

 

[merc estate]

13 years out a Varta, i was told that was the original battery on my old car and it did not fault once, so i got another one, simples.

 

[chic0821]

12.4v is 80% charged. Should be fine. I'm sure I posted this before, but here is a chart

 

[survey]

12.4v is 80% charged. Should be fine. I'm View attachment 117867sure I posted this before, but here is a chart

Thanks for this. Just returned from a 30 mile drive. Battery was 12.3 at start. On return I turned off ignition and checked voltage and it was 12.4. Then checked voltage with engine running and it showed 15.7 so alternator must be ok. Switched off ignition and immediately dropped back to 12.4. So just wonder if it is OK? Does this sound as though,using your data, its sound?

 

[chic0821]

I think its fine. If the car starts without any problems, just leave as is. We sometimes become fixated with problems that are not there. I am as guilty as anyone for this. If not using the car much, put it on a Ctek charger. My S63 lives on one all winter as near 600bhp & rwd isn't the best combination on slippery roads. Starts fist time after 5 months.

 

[190]

My experience is that unless it's a very long drive there is zero chance that a modern MB will finish a journey with anywhere near a 100 % fully charged battery. Smart alternators ensure that because they designed to drop the charging voltage right down when the state of charge reaches 80%. The only way you can ensure a 100% full charge, for the purpose of taking a 'state of charge' voltage reading, is with a battery charger followed by a minimum of several hours rest and the car definitely asleep. If the car is woken up even to take the reading it will drag the voltage down by several tenths. If you have done a rested voltage reading after a full charge and I think you have, then 12.4 volts is a very poor result for an AGM. It should be more like a minimum of 12.8 volts. I get 12.7 volts with my original non AGM Varta that is now 12 years old.

 

[survey]

My experience is that unless it's a very long drive there is zero chance that a modern MB will finish a journey with anywhere near a 100 % fully charged battery. Smart alternators ensure that because they designed to drop the charging voltage right down when the state of charge reaches 80%. The only way you can ensure a 100% full charge, for the purpose of taking a 'state of charge' voltage reading, is with a battery charger followed by a minimum of several hours rest and the car definitely asleep. If the car is woken up even to take the reading it will drag the voltage down by several tenths. If you have done a rested voltage reading after a full charge and I think you have, then 12.4 volts is a very poor result for an AGM. It should be more like a minimum of 12.8 volts. I get 12.7 volts with my original non AGM Varta that is now 12 years old.

Thanks. I had thought that after 30 mile drive the voltage would be rather better than before the start. I shall now recharge it to full with my credit agm charger and see what the resting voltage is after a few hours off charge. According to chico0821's voltage table 12.4 should be OK. Just didn't want to caught out with a car that fails to crank!

Incidentally my mb garage tells that disconnecting the battery to replace it and NOT providing a small charge to the pos and negative posts won't cause any problems. Has anyone any experience of this and its safe to swap batteries without any continuous charge applied?

 

[E55BOF]

I did the same job on my 2013 CLS recently, and one of the battery charger leads was disconnected for a second or two, but I didn't have to reset anything. Whether it would have been the same if it had been for a couple of minutes I don't know, but I'd think your MB specialist would be right.