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Which battery Eco start/stop draws off?

16K views 41 replies 8 participants last post by  cowboy45 
#1 ·
My Eco Start/Stop stopped stopping back in January, and between then and March (when we were all asked to stay a home), I had been driving it quite regularly.
I just assumed it stopped working because the battery won't hold charges (my console display does not have the yellow/green color change feature). Today, I climbed down the passenger side and checked the aux battery with my multimeter, and to my surprise, it was at > 13V (which I assume is a pretty healthy number).
I guess what I want to find out is: is Eco Start/Stop supposed to work off the aux battery? If so, sounds like I have another problem. Is there any way to "reset" it and try out first before I bring it to the dealer for some expensive surprises? Anybody knows?
 
#4 ·
There is a myriad of conditions for eco to work — many sensor data points and both batteries’ states of charge
Sometimes i wonder how it manages to work at all with so many status requirements
Anyway if the aux seems (?) ok, then a main battery soc check after an overnight sit may be an indicator
The headache is when both batteries are fine
 
#12 ·
jmc:

Thanks so much for all the advises - I climbed down the passenger side in the first place to check the fuses.. the little fuse diagram was alittle disorienting but to me, all looked ok (showed readings on my little multimeter)... as to a ctek charger.. I have never even heard of such a thing, I guess it is time for me to do some research.
 
#13 · (Edited)
i have migrated to the ctek mxs5.0 for my cars
decent unit with thermal compensation and auto desulphate
cute little gadget [emoji4]
( suggestion: wait for engine compartment to cool down somewhat before charging )
though after a few charge cycles and if no bad fuses ... if the eco still acts up then gonna need to see what benz specific stored codes exist
will be a dealer service visit ... or a good independent benz shop
 
#16 ·
Yes, very finicky. It seems to me that the battery has to be 100% charged for the Eco system to work consistently. Some of the models only seem to charge the battery whilst driving on the overrun, so you need a heck of a long drive to replenish a battery that hasn’t been driven much or has stood or has done short runs.
 
#27 ·
#25 ·
I had the same issue, but was testing the Aux after driving. Tested the following day ( overnight) tested low. Ordered new Aux and haven't had issues since. I live in AZ US and it gets hot! Burn through batteries quicker then normal. Spend the $200 first on the Aux before taking to the dealership. Same amount anyways.
 
#34 ·
Just to update you guys, I ended up putting in a new (primary, in the hood) battery - the (non-varta) battery is fairly good price so its just easier for me.
Eco start/stop started working immediately, stopping just about every time I press the brake - we all think auto-stop depends on various conditions,
but my experience made me start thinking its just the main battery's charge level (I know I know)

I replaced it myself, I knew it would be more difficult than what I saw on youtube (they all skipped a few steps) but it was yet quite a bit more involved
than I thought, though I'd say it's still quite manageable for laymen. You need a socket drive extension (or an anatomically incorrectly skinny and
long arm), brawns to lift and drop that almost 50lb monstrosity, and most importantly, know that to replace the plate that holds it in place,
you slide it through the gap between the battery and its enclosure (not the other direction); well, I cheated, I hoisted it down with a string so it
would land where it should, hey, whatever works, saves alot of money.

It was my first time so took me (and a help) a while, lost clock setting, trip meter, and my mpg history (never reset since the rubber hit the
asphalt), which is quite regrettable because I can never get that back; god forbid, all the bluetooth pairing survived - why that! I can always
pair again, I wish the aux battery had backed more important things.
 
#35 ·
Just to update you guys, I ended up putting in a new (primary, in the hood) battery - the (non-varta) battery is fairly good price so its just easier for me.
Eco start/stop started working immediately, stopping just about every time I press the brake - we all think auto-stop depends on various conditions,
but my experience made me start thinking its just the main battery's charge level (I know I know)

I replaced it myself, I knew it would be more difficult than what I saw on youtube (they all skipped a few steps) but it was yet quite a bit more involved
than I thought, though I'd say it's still quite manageable for laymen. You need a socket drive extension (or an anatomically incorrectly skinny and
long arm), brawns to lift and drop that almost 50lb monstrosity, and most importantly, know that to replace the plate that holds it in place,
you slide it through the gap between the battery and its enclosure (not the other direction); well, I cheated, I hoisted it down with a string so it
would land where it should, hey, whatever works, saves alot of money.

It was my first time so took me (and a help) a while, lost clock setting, trip meter, and my mpg history (never reset since the rubber hit the
asphalt), which is quite regrettable because I can never get that back; god forbid, all the bluetooth pairing survived - why that! I can always
pair again, I wish the aux battery had backed more important things.
Awesome! My local dealer quoted me $300 for the main battery (parts only). My battery shows 12.5 volts when not used. I also disconnected it and put a charger on it for a couple days to top it off. Eco still won’t work. I think there’s more than just charge level that makes it stop working. Based on your explanation, it sounds like it’s going to be a bit*h to change the battery.
 
#36 ·
The battery mass is the kicker
A cheap cantilever arm or engine hoist will help save your back
Battery in out aint so bad ... had to do that at a gas station once [emoji4] (at the 2yr mark)
And yes a few cluster readings are lost and windows may need a reset
And if its just the main battery causing eco issues then count your blessings ... there are many other sensors to check otherwise
 
#39 ·
well by "cheap" gadget i meant a lightweight one that folds up and hides in a corner ... looks like a crane arm
comes in handy for all sorts of stuff (especially tinkering on cars) like holding an engine up for mount work etc
and in this case removing and dropping in a >45lb battery ... i am getting too old for this $&!# :)
also holds all sorts of stuff for processing, painting, maintenance etc
something inexpensive, and not massive, like this example works wonders for safety and saving backs

66336
 
#40 ·
well by "cheap" gadget i meant a lightweight one that folds up and hides in a corner ... looks like a crane arm
comes in handy for all sorts of stuff (especially tinkering on cars) like holding an engine up for mount work etc
and in this case removing and dropping in a >45lb battery ... i am getting too old for this $&!# :)
also holds all sorts of stuff for processing, painting, maintenance etc
something inexpensive, and not massive, like this example works wonders for safety and saving backs

View attachment 66336
Thanks. I don’t think my wife will buy that explanation... women don’t understand why we need more tools. I’ll try to manhandle it and we’ll see.
 
#42 · (Edited)
Damn! I was always thought that all variants of CLA came with an AUX battery for ancillary functions like Eco Start/Stop (though I always keep eco off). However, I was so wrong when one morning my CLA 220 (2017 model, manufactured in mid-2016) would not crank at all. The battery voltage went so low that even car doors won't open using key-fob. Anyhow, I was able to jump-start and went straight to the authorized service centre.

On my way I was thinking, why did the AUX battery not enter the circuit if the main battery is down. Never a warning on the dash, nothing. Diagnostic engineer at the service centre said that my main battery needs to be replaced as it's 2016 made. Took $365 all-inclusive to replace the main battery. When I asked them about AUX battery, they said my car did not have one!

Later that day, I checked the footwell to confirm their claims, and indeed there was no battery, rather a small black box with part number engraved A2465409611 which houses 'VOLTAGE DIP FUSE'.

I did a little more research and came across this article which talks about how Daimler engineers were able to achieve the target of reducing cost and non-reliance on a backup battery without compromising on the efficiency of start/stop function. The article is called "Ignition current limiter replaces the backup battery concept"

I personally think it's very cheap move by Daimler. My Beamer never had this issue as core electrical always worked when either of the battery is in good condition. I wish my Benz had an AUX battery too! :rolleyes:
 
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