CaliBenzDriver

That seems like a very reasonable statement. Thank you for your excellent video, it flows well.

Do you have other maintenance item or troubleshooting on your list?
Happy holiday 🐇🐰

Adi-Benz

Thank you, and happy holiday!

At the immediate moment I'm doing a rotor/pad upgrade on my Chrysler 300, that will probably be next (I know, unrelated - fun note, a lot of things are shared between this and the W211 E class). As maintenance comes, I'll likely pick and choose what is more difficult or hasn't been talked much about and work on those. What is most likely next soon is some aesthetic upgrades on the CLS (parts shared with the facelift W212 and W205) so I will be sure to post here. Of course a sub is appreciated Thank you to those who watched my video and gave feedback!

Additional note: my biggest regret was not recording any of my maintenance and modifications throughout my ownership of my w204. But I kept it, so anything that comes up with that I will do as well. 722.9 transmission oil change soon....

kajtek1

When this charging system is not explored very far yet - all Aux batteries in MB are emergency batteries.
They are tested for voltage by charging module at each start and when charge is satisfactory, they get disconnected from the system, unless emergency will arrive.

bmwpowere36m3

What kind of emergency?

Later MYs with start/stop, i.e. the "large" battery in the trunk the OP changed is used specifically to keep the connivence functions running without glitching/restarting (due to voltage drop) when the engine is restarted during eco start. On earlier MYs the "small" dash battery seems to just provide a backup power source to the ignition to be able to shift the car into P/D/R/N if the main battery is dead.

kajtek1

This is the trunk battery we are talking about in this topic. It is not large as it is motorcycle size.
I can't find definite answer what in post-lifted W212 the mid-sized battery does. Suppose it is used for ECO restarts, but I see it too small for starter operation. Not even speculating if small cables running whole car length will supply enough juice.
Regardless what it does - the car will operate without it, with some functions disabled.

bmwpowere36m3

It wasn't a question, as much a statement. The trunk mounted auxiliary is much larger than the dash mounted one (which is the size of a home alarm backup)... two are mutually exclusive, either the car has one or the other. The trunk mounted auxiliary is NOT used to start the engine (for that matter neither is the dash). The trunk mounted auxiliary is wired to the rear SAM and is connected/disconnected as needed.

Left Coast Geek

the trunk battery on the eco start/stop cars is used to power all the vehicle ELECTRONICS during the start cycle, so the lights, stereo, etc don't blink when the enigine is started/restarted. if the stereo/nav system power was interrupted during the engine start, it would take 20-30 seconds to reboot again, quite annoying.

LILBENZ230

Main battery does seem to support start/stop in terms of system operation. Low main battery means the car will never shut off.

I always thought it was odd that nothing blinks during restart, but if you're using brake hold the brake lights go out and then come back on during the restart.

CaliBenzDriver

the way I see it... during ECO cycle the main battery supplies all consumers until the 100Amp starter gets involved to restart the engine then the loads get switched over.

All consumers get switched over to smaller trunk battery while the left over energy from front AGM is used ONLY to crank the starter while the trunk batt. keeps everything else "looking good".

At the point when the alternator is resuming duty both batteries need to be re-charged. The trunk battery charge current is mostly uncontrolled besides only by the resistance from the long feed cable during recharged.

Voltage, Current and Temperature are only mesured at the main AGM while the Rear-SAM keeps tab on the rear ECO Batt voltage to manage the near by ON/OFF relay.

An extra super cheapo Hyundai Korean sensor for ECO Batt would really not brake the bank to control working parameters.

​​​​​​​All I'm saying is Benz/Bosch well know
know what they're doing when they design uncontrolled chaos...(a big batt in parallel with a small batt... unlimited in-rush current... heat!)
NEEDS VENTING 🐰
🐇

pierrejoliat

So if I may, When you stop at a light then apply brake hold, the start-stop shuts down the motor, but the brake lights go out while your stopped at the light?
Damn, I will try that today on my pre-facelift today, I hope my brake lights stay on while I'm stopped at a light and use "Hold"

DFWdude

I've tried this myself some time ago, with someone outside the car to verify operations.

When you come to a stop, the brake lights are already lit, and remain lit. At a stop, the motor shuts down before you can initiate the Hold function... or change gears to Park.

So, on my car, safety lights do not go out while on eco stop/start mode. This thread is teaching me that the Aux battery is there (backup) to ensure that, while the main battery is primary for the motor restart (something I've concluded for a year, now).

KEY08

I know I have said this before, but the state of charge of the main battery is critical to the immediate operation of the ESS system. When I trickle charge the main battery my ESS will go green within the first couple of miles. If I haven’t driven for a week or so snd no trickle charge it may take 10-15 minutes of driving before the ESS goes green. The trunk battery does it’s thing to maintain the functions while the main battery is responsible for the continual restart after stop.

pierrejoliat

Interesting, I don't have Start/Stop so I was just trying to better understand what LB was saying. Let me ask this; If you come to a stop and engine shuts off before hold function is activated, do you have to keep your foot on the brake? Or do you activate the hold function at that point?

KEY08

The car will shut off as soon as you are a nanosecond before stopping completely. As soon as it senses you are lightening up on the brake, the car starts. It’s very sensitive. I don’t ever really use Hold so not sure how that affects the ESS operation.

pierrejoliat

Oh wow, I use brake hold all the time, I just checked, my brake lights stay on with the car in drive and brake hold activated. Also, if I turn the key to second position and let NAV boot up, when I turn key to start my screen goes black for a second, then comes back on.
I assume that is not the case in the facelifts with a trunk battery.

DFWdude

The brake light is on, with or without the Hold function. Eco Stop/Start shuts the engine off before I notice it, so it's always a surprise to me. Since you have your foot on the brake when this happens, you need only to add the extra brake pressure to initiate Hold mode (while the engine is off). Then you can take your foot off the brake... Hold is active and the brakes are lit, even though engine is off. When the traffic light turns green, just put the foot on the gas, and the engine restarts, Hold is canceled and the brake lights go out... all within a few milliseconds.

The only part that takes some adjustment is anticipating a slight lurch forward, since the engine restarts while your foot is on the gas (and not on the brake). I minimize the jump by being light on the throttle. Not the best for a crisp getaway from the stop. But I still have concern about engine wear if the car jumps off the line bigtime while it is restarting. Hope that makes sense.

pierrejoliat

Yes, I think I have it now, thanks for the info! Interesting with that kind of stop/start and using the gas pedal to restart, it would also start out in first on the facelifts, when I'm in sport, which is admittedly rare, I have to be really careful to modulate the gas to avoid a very jerky start and the car is shifting to second in about a lane width, I guess you get used to that. Mine both start in second in "E"

Fliplegend

Got the "Auxiliary Battery Malfunction" today on my 2016 E350 and went ahead and ordered the MightyMax battery thanks to Adi-Benz and this thread.

kajtek1

The 4-cylinders in my E250 Bluetec don't do the jump on restart, like Dude is experiencing with his bigger engine. Still amazing how everything is ready to perform in milliseconds. But what I learned about the system - transmission is having aux electric pump, so it keeps fluid ready to restart, and in case of my diesels, the rail keep operating pressure, so seems the engine restarts mainly on electronically -controlled fuel injection when piston doesn't move. Starter is only backup, to avoid reverse turn.
But lately I bought GLE with the same 4-cylinder diesel and the car has a program who is revving engine high on 1st gear. (diesels always start on 1st) and that can be annoying as I just barely touch accelerator pedal and the engine will go above 3000 rpm on 1st and then will respond to actual pedal movement on following gears.
After noticing that on GLE, I start paying attention on E and it does rev higher on 1st gear, but only slightly, so I did not notice it before.
With computers opening new possibilities, I concluded that MB made the software for small engines that gives you impression of bigger HP that it actually has.
I prefer to be in command of my vehicles and don't like when stupid computer takes over, but there is no way to change it.