Daytona-flyer

There is what looks like a second battery in the trunk. I've heard it's for the ECO start. However with the ECO engine starts, there is no sound of a starter. I understand that certain cylinders, those at, near or just past TDC, fire to get the engine start after an ECO stop.

Any input on this?

jpeardm

The second battery only supports the electrical system while the motor is off in ECO mode.

Gunther

Exactly, MB has been running a two battery system to support the extra load that the cars have for years. My 2004 has two batteries. It can also work to start the car should the primary battery be too weak to start the car on its own.

BillyD

The second battery is behind the passenger seat in the cockpit.
The "primary" (95AH) battery is the one in the trunk.
And yes, the secondary (small) battery behind the passenger seat is for the ECO start/stop system.
In previous SLs (e.g. R230) the primary battery was also in the trunk. The smaller (secondary) battery was in the engine compartment and was reserved for the starter and engine electrical needs only.

Daytona-flyer

Both batteries in mine, are next to each other in my trunk below both partitions. Both batteries are mounted sideways with the main battery in the center. The second battery is to it's left, behind the driver.

red308

On mine the starter can be heard on an ECO startup. But just barely. I think the way they fire the appropriate cylinder makes it start up so fast that you can almost not even hear the starter. But it is definitely turning the motor over.

BillyD

That is incorrect. What you are describing as the second battery is not a battery. I believe that it is the hydraulic pump mechanism for the vario roof.
In any case, it is not the second battery.
The second battery is exactly where I said it is.

ajm0623

like red308, i can hear my engine fire up as well after shutting down due to eco. it is not horribly loud but can definitely tell it is firing up.

Daytona-flyer

Well the box next to the battery looks sort of like a battery box. Read my first post.

Is the second battery in the passenger side storage compartment, behind the seats, that doesn't open?

ajm0623

my passenger side compartment (behind the right seat) opens. you first remove the vertical panel then proceed by removing the horizontal panel.

Daytona-flyer

Thanks. I opened it and even found the page in the manual. The battery must be quite small.

BillyD

This is the post you made to which I reacted.

I'm pleased that you now know that the battery is where I told you it is.
Hope my posts helped you.

Daytona-flyer

No need to react negatively. I just wanted to know what the box was next to the battery. I asked my service advisor at M-B the last time I was there and even he didn't know.

ajm0623

huge learning curve on a new model like the 2013 sl550. for everyone alike: owners, salesman, mechanics, etc. part of the (a-hem) "charm" of owning a first run batch of a new chassis model. we'll all get there.

BillyD

The key to information is to clearly distinguish, when posting, between what you actually know to be a fact and what you think.

There is a tendency, especially with salesman, to bluff (guess) at the answer.

At a Palm Beach County MB dealership, for example, a so called top salesman asked me what vehicle I was talking about when I asked a question about my SL and I had referred to it as a R231.

I put a very high value on those who communicate factual information secured only from a proven reliable (usually written) source. Some questions are hard (e.g. how does the SL ECO stop/start really work?).
Some questions are really easy (e.g. where is the 2nd battery?)
The later is not a learning curve question, it's in the owner's manual.

MBtech1098

Close but not exactly. The ECO start/stop battery G1/13 actually only supports active electrical loads during the brief starting sequence when ECO start/stop is active. During this time the main battery, G1, is isolated from the rest of the vehicle to allow full power to the starter armature only. The starter solenoid power still comes from G1/13 in this case. Of course with ECO start/stop the starter is not the only thing used to start the engine.

The 230 dual battery system is quite different. The trunk battery aka systems battery aka G1 provides power to all electrical loads of the vehicle under normal conditions with the exception of the starter armature. The front battery aka starter battery aka G1/4, only provides power to the starter armature, the solenoid for the starter is still powered by G1 under normal circumstances.

Normally these two batteries are completely isolated, only for charging or undervoltage are they linked in parallel by battery cutoff relay K57.

Once again see previous quote, under normal circumstances the starter battery powers ONLY the starter armature.

Daytona-flyer

Why don't I hear the starter motor when the ECO restarts the engine? All I hear is chug-chug and the engine starts.

MBtech1098

Because the starter is not always needed. On vehicles with ECO start/stop they use a different crank position sensor. This sensor is much more exact and knows precisely where each cylinder is in the 4 stroke process. The MED 17.7 analyzes that information, if it sees a cylinder at TDC compression it will first inject fuel into that cylinder and then ignite it. This of course starts the engine. However if none of the cylinders are in the right position for the start sequence, the starter will "bump" the engine to the correct position.

This is the reason you don't hear the starter as it is never really making a full revolution in the ECO start/stop process.

jpeardm

MBtech, thanks for all the clarification on the ECO, I'm sure others appreciate it as well.

Daytona-flyer

Thanks, that was a clear explanation. This car is still a mystery to me.

wings

My 2013 Sl63 has a hidden, very small, second battery behind the passsenger seat. ITs sole purpose is to provide electrical power to the transmission and allow the selector to be moved into or out of park should the main battery fail. Other then that there is really only one battery for everything else.

California John

Hi Wings,

What can you tell us of your SL63? How is it configured and how does it handle?

MBtech1098

Partially correct, that second battery is known as G1/13. I did forget to mention that this battery also will provide power to the Inteligent Servo Module (ISM A80) in the event of On-board electrical systems failure. This however will only engage park and is done so automatically once the key is removed from the ignition switch (EZS N73). For vehicles with KG park is engage once the driver door is open. It is known as a fail safe and will not allow you to disengage park.

The transmission still receives it's power from the main battery G1.

Please reference the following WIS documents:

GF07.10-P-1041MMF - Engine Control Start/Stop function
GF54.10-P-1040RK - ECO Start/Stop energy Management
GF27.10-P-3029AHJ - ISM Emergency P function

Web ETM:
PE15.00-P-2103RKA

*Note: This is only for vehicles with SA code B03 ECO Start/Stop. Vehicles without ECO (ie: other countries) will still have a seperate battery G1/7 which will serve the same function for the ISM.

BenzV12

Thanks for everyone for your informative replies
It never dawned on me that 2nd battery would provide enough power for such things just in case , what an engineering marvel
Thanks , MBTech for your replies as well

wings

Hi California J. With just 600 miles on it I have been going by the book for the break in period. I traded my 2004 SL600 and this car feels and is much more luxurious. The steering feel is good especially when you select S or S+. I was concerned about the new electric steering feature. The noise is great, just like the reviews say it sounds like a Nascar Race Car although I have only been up to about 4500RPM and I expect it will get better. I have to put a few more miles on it before I can give a real report as I am still in the "new"stage. Silver car with red and black interior.