Battery Replacement

[survey]

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, though.

Thanks. That's encouraging. I had been told to put a charger on the two external posts whilst changing batteries to avoid having to reset the folding mirrors and the clock. But maybe even this isn't necessary then? Getting the battery out and inserting another in that right space won't be easy and worse if there are charging clips on the posts!

 

[survey]

Thanks. That's encouraging. I had been told to put a charger on the two external posts whilst changing batteries to avoid having to reset the folding mirrors and the clock. But maybe even this isn't necessary then? Getting the battery out and inserting another in that right space won't be easy and worse if there are charging clips on the posts!

'tight' space, not 'right space!

 

[190]

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?

That table looks to me to be applicable to a normal battery not an AGM which I'd expect to be at least .1 or .2 volts higher at every step. Battery chemistry changes subtly all the time such that there is no longer any such thing as a standard lead acid battery. Most of the tables available on line are not as accurate as they once were because they were based on older standard battery chemistry.

While 12.4 volts will start the car, if that's the best a fully charged AGM can produce then it's indicative of a battery getting to the end of it's life. AGM rested voltage does fall a few points over the years even when the battery is still reasonably healthy but not by that much. I have an AGM on the bike which was reliably 13.05 volts when new (see what I mean about the tables) and is now down to 12.8 or 12.9 volts at 8 years old.

I've had the battery disconnected overnight and the only thing I noticed was the mileage trip zeroed itself. It's a basic car though with no memory seats.

 

[survey]

That table looks to me to be applicable to a normal battery not an AGM which I'd expect to be at least .1 or .2 volts higher at every step. Battery chemistry changes subtly all the time such that there is no longer any such thing as a standard lead acid battery. Most of the tables available on line are not as accurate as they once were because they were based on older standard battery chemistry.

While 12.4 volts will start the car, if that's the best a fully charged AGM can produce then it's indicative of a battery getting to the end of it's life. AGM rested voltage does fall a few points over the years even when the battery is still reasonably healthy but not by that much. I have an AGM on the bike which was reliably 13.05 volts when new (see what I mean about the tables) and is now down to 12.8 or 12.9 volts at 8 years old.

I've had the battery disconnected overnight and the only thing I noticed was the mileage trip zeroed itself. It's a basic car though with no memory seats.

Thanks for this. Food for thought!

 

[chic0821]

Type in "battery voltage cigarette lighter" to ebay. Small plug in reader into the lighter socket (assuming you have one), around about a fiver. Gives you an continual readout to keep a track of your voltage at any given time.

 

[OneForTheRoad]

If all the windows are up , just change the battery . No need to faff on . The charging posts you've been told about won't be in your way ,if you did connect up a charger .

 

[survey]

If all the windows are up , just change the battery . No need to faff on . The charging posts you've been told about won't be in your way ,if you did connect up a charger .

Thanks for this. So I don't need to maintain a charge whilst battery is disconnected?

 

[OneForTheRoad]

Thanks for this. So I don't need to maintain a charge whilst battery is disconnected?

No.

 

[geoffus]

I did a short write up changing my battery, I connected a small battery whilst changing over, but you don't need to.

New Battery cured Stop Start. | Electronics and Audio

The original battery on my E250 was dated 2014 and began struggling recently to start he car. The stop start function had also stopped working so main battery looked suspect. Just had a new battery arrive and promptly fitted it. Stop Start is now back to fully working and the Eco button goes...

forums.mbclub.co.uk

 

[markjay]

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?

The battery has clearly degraded, but it's still fine. It will probably be good for a couple of years. Just keep monitoring the voltage, to avoid a nasty surprise one very cold morning.

Also, if your car is equipped with Start/Stop, it will stop working at some point, but the battery will still be good for cranking after that.

That said, nothing wrong with just getting a new battery, given that this one has done job.

 

[survey]

The battery has clearly degraded, but it's still fine. It will probably be good for a couple of years. Just keep monitoring the voltage, to avoid a nasty surprise one very cold morning.

Also, if your car is equipped with Start/Stop, it will stop working at some point, but the battery will still be good for cranking after that.

That said, nothing wrong with just getting a new battery, given that this one has done job.

Thanks. I'm rapidly coming to that conclusion. Will check resting voltage from time to time. Will probably replace battery when it's convenient yo do so but hopefully no rush! The responses regarding not having to worry about maintaining power to the system when changing batteries is a relief!. Would have hated to have to reset electronics, radio, seats, windows......!

 

[colinallcars]

Thanks. That's encouraging. I had been told to put a charger on the two external posts whilst changing batteries to avoid having to reset the folding mirrors and the clock. But maybe even this isn't necessary then? Getting the battery out and inserting another in that right space won't be easy and worse if there are charging clips on the posts!

The charging clips should be on the jump start posts under the bonnet, not on the battery posts therefore not in the way.

 

[survey]

The charging clips should be on the jump start posts under the bonnet, not on the battery posts therefore not in the way.

Yes know that but just wasn't sure if they would interfere. Thanks.

 

[Uky]

Replacement strategy adviced by a friend who worked for MB
and used by me when replacing the battery in my C207:

Pull the driver side window down.
leave the doors unlocked.
Turn off everything.
Keep all Keyless keys well away from the vehicle.
Open the engine hood.

Wait for ~ 20-30 minutes for car to go into sleep-mode.

Replace the battery beginning with the negative pole and
ending with the same.

(While you are at it, remove the battery mounting plate and check for rotten leaves etc
underneath. WARNING: One of the bolts are deliberatly short since an aluminium
tube runs directly underneath. Replacing with a longer bolt will crack the tube!)

If properly done, all calibrations of windows, sun roof etc should be as they were.

The general advice for anyone doing something with the electric system is to ALWAYS
have the driver side window down. Should the keys vs control box go into a "f-d up state"
there is always a way to get inside the car to gain access to the OBD outlet, etc.

 

[survey]

Thanks to everybody for their posts. Since charging the battery, it has always started the car and a resting voltage of 12.4v is being maintained. I have a feeling that I left the drivers door open for some time and then when I came to start the car ir wouldn't crank.

So for the time being my 9 year old battery is operating OK. I will check on it from time to time but it would appear that it's sound enough at present. When it comes to replacing the battery I will take take note of the recommendations made in this post.

Thanks again all!