It is FYI: Start/Stop is not working, ECO is green. Can't tell if it is the battery or something else. The time will tell.
Back ground:
It is 2018 43 AMG, 111km/70Kmiles. The ECO was not working since I got the car in 2021 (60km/37Kmiles) under CPO until Oct 2024 or 120km/75Kmiles. Actually, it worked for a few weeks after visiting the dealers and than stopped working. The ECO light is always green and no error message. Full disclosure here, I don't like the ECO. When it works -- mostly, I turn it off. Went to dealers 3 times over the years, and they could not find anything wrong under warranty. Second visit, dealer replaced aux battery under warranty in Spring 2023. The third visit, they wanted over $1000 + 13% tax ($450 for battery + 2.5hr labor, ~ $250/hr in GTA/Toronto) to replace main battery in Fall 2024 just before out of CPO warranty. The main battery is considering as wear and tear; therefore, it is not covered under warranty or CPO warranty. I consider the price is fair, but I don't like the up sale from SA, fear/threat with safety issue, and probably may not fix the issue, i.e. parts cannon. Also, I am too cheap/poor and can't justify the 2.5hr for labor, especially, when you do it every day/every often. I understand that it is a stealer policy -- either you bend over or no with thank you/walk away.
I said no and thank you. Off I go, I drove another Winter. I decided to replace the main battery in Apr 2025 -- 7 years is a good run. I got the Energizer battery from Costco for $430, made in German. By Aug 2025, the ECO is not working again. No error message and the ECO led is lid green all the time, just not working. By Dec 2025, the dash cam and radio works for about 10-15 minutes before turning off to safe the battery. In Jan 2026, it was hard to start and needed to press a few times when temperature dropped below -25C/-13F -- parked out side, daily drive 16km/10miles, and weekend 50km/30miles.
In Jan 2026, I got a Youcanic scanner over $1K (>$150 for tariffs, Ouch!). Scanned and cleared a few times, still got B21059A error code and the 39A charged resistance for the main battery. Still no change and ECO is still not working after replacing Aux battery with LiFePO4 12v8Ah. In Mar 2026, I decided to replace main battery -- EverStart from Walmart, made in Austria, $230. Scanned and cleared, the battery resistance came down to 9A, error code B21059A is gone and ECO is working for now. The time will tell.
Please note, LiFePO4 12v8Ah is NOT FIT into OEM aux battery's bracket. It is bigger than OEM Aux battery. I removed the bracket and used hot glue gun with heavy duty Velcro tape. The LiFePO4 should last 10 years if everything is working well. The stealer wants $160 + 13% tax for OEM Aux battery, 12v 1.2Ah. I hope this would help the others who may have this kind of issues.
Seems like the electrical system is getting buggered. Multiple batteries and a dash cam. What else? Remove all of the extra add ons and replace both batteries. Then update this thread.
Why did you substitute a lithium battery for the OE lead acid battery? Is it spec'd as a suitable direct replacement? There are inexpensive replacement alternatives to the dealer's (
). A larger capacity battery won't remedy an electrical fault.
Before I acquired an OBD scanner to code off permanently the annoying start/stop, I disconnected the main battery current sensor (a small black box hanging on the battery's negative terminal) which made the ECU think the battery charge level couldn't sustain repeated engine starts. However, OBD scans always reported an associated fault code. Perhaps your battery sensor is intermittent -- a faulty or corroded connection(?).
Seems like the electrical system is getting buggered. Multiple batteries and a dash cam. What else? Remove all of the extra add ons and replace both batteries. Then update this thread.
I confirmed over the years that the dash cam is not the issue and it has cut off power supply when the battery drops below 11.8v. I replaced/returned the energizer main battery due to high resistance and had a hard time to start when it is cold. I just replaced both batteries a few weeks ago. As matter of fact, I don't mind if the ECO is not working over the years. But the high resistance may cause the alternator works harder to charge the battery that could led to shorter life of for the alternator.
Why did you substitute a lithium battery for the OE lead acid battery? Is it spec'd as a suitable direct replacement? There are inexpensive replacement alternatives to the dealer's (https://www.amazon.com/Yuasa-NP1-2-1.../dp/B00FA61J54). A larger capacity battery won't remedy an electrical fault.
Before I acquired an OBD scanner to code off permanently the annoying start/stop, I disconnected the main battery current sensor (a small black box hanging on the battery's negative terminal) which made the ECU think the battery charge level couldn't sustain repeated engine starts. However, OBD scans always reported an associated fault code. Perhaps your battery sensor is intermittent -- a faulty or corroded connection(?).
I don't know about the MB spec for lithium and lead acid. The reason that I replaced with lithium so that I don't need to worry/lazy to replace the aux battery for another 10-15 years. For Aux battery is not an issue with cold weather or charge issue. The main battery may have issue with low temp (like -25C/-13F) with quick draw current to start the car and charge/discharge the battery at low temp. If you live in the warmer area, I don't see the issue. It's much less weight to work with and last longer (10-15 years).
Next step would be the battery sensor or capacitor like the recall with GLA/C recall.
I checked and confirmed the battery sensor at the negative terminal for corrosion and connection. I cleaned/checked (wire brush/sand paper) battery terminal and cable too many times over the years.
I don't know about the MB spec for lithium and lead acid. The reason that I replaced with lithium so that I don't need to worry/lazy to replace the aux battery for another 10-15 years. For Aux battery is not an issue with cold weather or charge issue. The main battery may have issue with low temp (like -25C/-13F) with quick draw current to start the car and charge/discharge the battery at low temp. If you live in the warmer area, I don't see the issue. It's much less weight to work with and last longer (10-15 years).
Next step would be the battery sensor or capacitor like the recall with GLA/C recall.
I checked and confirmed the battery sensor at the negative terminal for corrosion and connection. I cleaned/checked (wire brush/sand paper) battery terminal and cable too many times over the years.
FYI, in a properly working system. My stock main lasted 11 years and the aux lasted 13ish. Something is wrong with the system with all these replacements. Have you done a complete draw test? As well as checked the mentioned connections?
I don't know that this contributes anything to the overall issue but as far as the ECO start/stop is concerned, the aux battery (the smaller one that's located behind/under the left rear seat) is a major player in that function. So if you're having trouble with the ECO start/stop, that battery, the wiring and connections attendant to it would be a good place to start looking.
FYI, in a properly working system. My stock main lasted 11 years and the aux lasted 13ish. Something is wrong with the system with all these replacements. Have you done a complete draw test? As well as checked the mentioned connections?
Thank you. Good to know. I am about to work on 2018 GLE 400 -- same issue, ECO is not working, ECO is lid green, B21059A, high resistance/30A. But my wife didn't complaint regarding start up in the morning when temp dropped below -25C/-13F. Now, she pushes the red button to work on it since the gas price over $1.79/L for 87 octane -- (+20/25c for 91) in Toronto. I don't see much of saving regarding to gas for ECO either working or not.
No, I have not done the current draw test. It is not come to the point that I need to do/trace for the root cause yet. I already got the Aux battery (12v6Ah is a bit smaller than 12v8Ah for GLE 43) and wait for a warmer weather to work on the GLE 400. For GLE 400, I don't know if both main & Aux batteries had been replaced, but carpet was not cut though.
I don't know that this contributes anything to the overall issue but as far as the ECO start/stop is concerned, the aux battery (the smaller one that's located behind/under the left rear seat) is a major player in that function. So if you're having trouble with the ECO start/stop, that battery, the wiring and connections attendant to it would be a good place to start looking.
In my case, the ECO is not working and ECO led lid green -- i.e. no error code for ECU or lid yellow. Overall, the car sees as okay/working, but the engine never turn off even after driving a few hours on free way. But, there is code B21059A (not on dash) with high resistance/30A. No, not just Aux battery is responding for ECO start/Stop. The main battery needs to be more 65-85% of full charge in order to work. If the main battery is less 65% of full charge, then ECO will not work (it is one of the main condition for ECO to work). The battery is asking for 30A from alternator to charge, and the ECU sees as less than 65% of full charge as preset condition, i.e. death locked condition in term of software/firmware/programing.
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