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Please explain this Standby Mode option. I don’t want to use the car for two months. The 12volt battery is fully charged and the 6 volt battery was replaced 6 months ago under warranty.
The car won’t go into standby mode stating that the battery level is too low. Which battery?
What should the voltage be on which battery?
I’m not even clear on the purpose of the 6 volt battery.
No modern Mercedes has any 6 volt battery. Are you referring to the small motorcycle battery (start/stop battery)?
Did you charge the main battery with a maintenance charger or just by driving the car? Is it not possible to have the car connected to a maintenance charger for the 2 months time? The battery would not survive 2 months in normal mode. Not sure if it would in standby mode (alarm and everything possible deactivated).
In my previous car, a C350, the auto-stop function worked dramatically better after giving the 12V battery a lengthy charge. As I understand it, AGM batteries take much longer to fully charge. I had a battery place charge it overnight and when I came back the next morning they tested and said it would benefit from still more charging, so that's when I took it home and put it on my charger for another full day.
Once charged in this manner, auto-stop would occur almost every time and the actual restart was quick and nearly unnoticeable, close to the way it works on our Honda hybrid.
The battery in my S550 is apparently the original from 2016 and the car rarely auto-stops, so I suspect it's nearing the end of its life and I plan to replace it.
Last edited by Tom in Austin; Feb 3, 2022 at 08:15 AM.
I thought that battery was 6v? Regardless, I've driven the car in an attempt to increase levels and also charged the 12v battery and still get the same message of low charge.
Should I attempt to charge that start/stop battery?
I didn't have any messages in my cars, just aging main batteries and infrequent auto-stop. Maybe the dealer can interpret the stored codes in your case to make a better diagnosis of what's needed.
Or if you know your battery(ies) is/are old, you might just replace it/them proactively and see what happens. Costco here has an H8 AGM for $178 which is a pretty good price, so I will just put in a new one when I work myself up to lugging that 61 pound beast back and forth :-)
I didn't have any messages in my cars, just aging main batteries and infrequent auto-stop. Maybe the dealer can interpret the stored codes in your case to make a better diagnosis of what's needed.
Or if you know your battery(ies) is/are old, you might just replace it/them proactively and see what happens. Costco here has an H8 AGM for $178 which is a pretty good price, so I will just put in a new one when I work myself up to lugging that 61 pound beast back and forth :-)
If I got it right, the OP was talking about the standby mode that only exists in the very latest MB models. I assume your car does not have it and would not through the same error messages as for the OP. Your point still makes sense as the car even does not want to charge the main battery to 100% level but a maintenance charger would do it (the car wants to leave some battery capacity for recuperative braking, it happens via the standard alternator even on non-EV or non-hybrid cars).
The battery is over 4 years old and I'm surmising that its at its end of life.
I will replace the battery and I'm reaching out to see what method is best to replace the battery without losing power to the electronics.
Good point Diesel, even though we're both W222s, the facelift cars have many changes and I forgot that 'eco' mode on the newer cars includes cylinder deactivation and possibly other functions. My experience with the '16 (and before that with a '14) is just auto-stop and may or may not be relevant to the OP's issue.
I thought that battery was 6v? Regardless, I've driven the car in an attempt to increase levels and also charged the 12v battery and still get the same message of low charge.
Should I attempt to charge that start/stop battery?
Indeed, the stop/start battery voltage does not make any difference here. I'm afraid the car would need to be diagnosed if it is not willing to activate standby mode. I don't know if low charge level on the stop/start battery could disable standby mode. Would not harm to charge it with a maintenance charger but accessing the battery isn't straightforward.
The aux battery (or capacitor in some cars) functions primarily to operate lights and accessories while the engine is off. It does not have a direct role in re-starting the engine following auto-stop, the big battery spins the starter motor. However, the system will not go into auto-stop to begin with if it thinks the aux battery has insufficient charge. So in reality, either or both batteries could prevent auto-stop from working since they have different roles in the process.
The aux battery (or capacitor in some cars) functions primarily to operate lights and accessories while the engine is off. It does not have a direct role in re-starting the engine following auto-stop, the big battery spins the starter motor. However, the system will not go into auto-stop to begin with if it thinks the aux battery has insufficient charge. So in reality, either or both batteries could prevent auto-stop from working since they have different roles in the process.
Quite correct for start stop operation but the aux battery has no role in standby mode. The intention of standby mode is to reduce the battery consumption to absolute minimum when the car is parked for a long time. The aux battery has no load when parked and there is no need to reduce the aux battery load then. However, the aux battery should have sufficient charge to survive from internal leaks. Very marginal and I would guess aux battery state not preventing standby mode but this is just a guess.
Throwing in some information. So yes the standby mode turns everything off to allow the car to be parked for an extended time. Particularly it turns off the permanent Internet connection that these cars maintain otherwise in order for remote start/lock/unlock/status to work. But like a cellphone that will slowly drain the battery over time, so standby mode will power everything off, and also tell you how long you can keep the car parked w/o the battery needing to be charged, but as you observed, the battery needs to be charge sufficiently in the first place. As others have said, AGM batteries take a while to fully charge and the alternator never actually fully charges them to leave some room for recuperation. When you are off throttle, the alternator voltage is increase to recuperate some of the energy into the 12V battery that can later be used to power the electric consumers and save fuel. The Mercedes me connect app shows you if the battery is partially charged or fully charged, but that doesn't really give you any specifics. You can get a real-time readout for the battery through the vehicle data in the workshop menu, such as voltage and current draw. If your voltage has dropped below 12V even after a full charge with a trickle charger, then your battery needs to be replaced. 3-4 years is average battery life these days depending on how the car was used and where it was parked. If parked outside in the cold during the winter, you'll get less out of the battery than a garage kept car, or a car driven mostly in mild climates.
I think this feature was added starting MY 2018 and up. I've never used it in my cars as I just pop open the hood and leave the battery on a battery maintainer when the car is left months at a time without being driven.
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