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Hi All, I have a new to me 2020 GLC300 mild hybrid. (Eqboost)
I noticed the 12v battery was partially charged in the Mercedes ME app and so I am looking to charge it. I looked under the vent towards the top right of the engine bay (under the filter) and it seems to be the 48v battery.
Is the standard 12v battery in the boot ? or somewhere else?
Presumably I need to use the jump connectors under the bonnet to charge the 12v battery (this is what the manual suggests, but doesn't differentiate between the models), and set the charger to AGM mode (as everything points to the 12v battery being a 096 AGM battery) which in turn charges the 48v battery via a built in convertor?
Let's save you from all the hassle by just starting the engine and letting it run, preferably not in a garage though, or take the vehicle for a trip around town if you don't want to just let it idle. That way, your 12V battery will get charged.
Yes, charging is through the terminals under the hood. However, partially charged doesn't mean that you have to charge it. It will show partially charged fairly quickly, which just means it's not fully charged. Most batteries spend their entire life partially charged if you think about it. Nothing to worry about. If the charge gets too low you'll get notifications through the app and via email to let you know. You can leave it sit at the partially charged level for quite a while. If the car is parked for an extended period then you can activate the standby mode. It's not available on all models, so you have to check. But standby mode turns off the online services, so that the battery isn't drained by the car maintaining a connection to the Internet while parked. It also has the nice side effect of telling you exactly how long you can leave it parked before the battery needs to be charged. I use the standby mode when going away for a few weeks. Most of the time my battery says partially charged, unless I've been on some long drives recently. I have gotten some critical battery alerts while the car was in service, but I know make sure the battery is fully charged before I take it in and so far that has worked. I do that by either going for a long drive or hook it up to my battery maintainer the night before, but otherwise I mostly drive only on weekends, so it sits usually for up to week in the garage. If you do only drive short distances then you might need to eventually hook it up to a battery maintainer, but only if you start get critical battery alerts.
Last edited by superswiss; Sep 20, 2022 at 08:47 PM.
Let's save you from all the hassle by just starting the engine and letting it run, preferably not in a garage though, or take the vehicle for a trip around town if you don't want to just let it idle. That way, your 12V battery will get charged.
Unfortunately, it must just be below that point, as I drive it alot and it does switch from partial to charged but you leave it overnight and it's back to partial. I think it's just that step too discharged. So I want to bring it back fully, so then it can maintain the full charge.
Yes, charging is through the terminals under the hood. However, partially charged doesn't mean that you have to charge it. It will show partially charged fairly quickly, which just means it's not fully charged. Most batteries spend their entire life partially charged if you think about it. Nothing to worry about. If the charge gets too low you'll get notifications through the app and via email to let you know. You can leave it sit at the partially charged level for quite a while. If the car is parked for an extended period then you can activate the standby mode. It's not available on all models, so you have to check. But standby mode turns off the online services, so that the battery isn't drained by the car maintaining a connection to the Internet while parked. It also has the nice side effect of telling you exactly how long you can leave it parked before the battery needs to be charged. I use the standby mode when going away for a few weeks. Most of the time my battery says partially charged, unless I've been on some long drives recently. I have gotten some critical battery alerts while the car was in service, but I know make sure the battery is fully charged before I take it in and so far that has worked. I do that by either going for a long drive or hook it up to my battery maintainer the night before, but otherwise I mostly drive only on weekends, so it sits usually for up to week in the garage. If you do only drive short distances then you might need to eventually hook it up to a battery maintainer, but only if you start get critical battery alerts.
Thanks and is yours a eqboost, so it has the 48v and 12v system ? Do you put your charger on AGM mode ?
Thanks and is yours a eqboost, so it has the 48v and 12v system ? Do you put your charger on AGM mode ?
No EQ Boost. My car is a '19 C63S. I don't do eco anything . My charger automatically detects the battery type, but yes it switches to AGM mode. Most Mercedes have an AGM 12V battery now and a few have lithium batteries, which requires a charger that supports lithium batteries.
No EQ Boost. My car is a '19 C63S. I don't do eco anything . My charger automatically detects the battery type, but yes it switches to AGM mode. Most Mercedes have an AGM 12V battery now and a few have lithium batteries, which requires a charger that supports lithium batteries.
Ah yes, so yours will be 12v only and not whatever blend Merc have put in this mild hybrid combo. I think I will need to find a friendly specialist who can share the Intel if where is that pesky 12v battery hiding !
No EQ Boost. My car is a '19 C63S. I don't do eco anything . My charger automatically detects the battery type, but yes it switches to AGM mode. Most Mercedes have an AGM 12V battery now and a few have lithium batteries, which requires a charger that supports lithium batteries.
Thanks, I think this has both a 48v lithium and a 12v AGM as its the EQboost. Seems like this specific system is not well known yet and I will just need to ask Merc or a Specialist the next time I am around one. I am betting that there is either the separate 12v to the 48v or they have merged both into a single unit.
In the Merc technical guides, it does say the 48v only gets charged via the 12v with a built in convertor and it's not possible to directly charge the 48v lithium...but no more.
Unfortunately, it must just be below that point, as I drive it alot and it does switch from partial to charged but you leave it overnight and it's back to partial. I think it's just that step too discharged. So I want to bring it back fully, so then it can maintain the full charge.
I see, do you drive long distances per trip though or you do a lot of frequent on/off but like superswiss mentioned, partially charged is not a concern, only when it says battery level critical is when you have an issue, if I recalled correctly, partially charged just means battery has dropped down to 80%.
I wonder if the auto start/stop is also putting strain on your battery (as I am not fully sure if your vehicle has the electric starter or the traditional starter even though it is a mild hybrid hence pulling power from the 12V, superswiss, do you have more information?)
EQ Boost uses an ISG, so start/stop won't matter. Just to reiterate, partial charge is not a concern. AGM batteries charge slower than the old lead acid batteries, but they are much better at powering all the electronics in modern cars. The main reason you see the battery charge drop is because these cars don't fully turn off. They are like a cellphone in some ways. The connection to the Internet and telematics stays alive, so that you can remote lock/unlock/start and check on the status of the car. That's where the standby mode comes in. It doesn't hurt to periodically fully charge the battery if it has sat for a couple of weeks, but not when it goes to fully charged from normal driving and then just drops back down to partially charged.
Last edited by superswiss; Sep 21, 2022 at 10:12 AM.
I see, do you drive long distances per trip though or you do a lot of frequent on/off but like superswiss mentioned, partially charged is not a concern, only when it says battery level critical is when you have an issue, if I recalled correctly, partially charged just means battery has dropped down to 80%.
I wonder if the auto start/stop is also putting strain on your battery (as I am not fully sure if your vehicle has the electric starter or the traditional starter even though it is a mild hybrid hence pulling power from the 12V, superswiss, do you have more information?)
A mix really, sometimes short, sometimes 40 min and other times 2 hours.
EQ Boost uses an ISG, so start/stop won't matter. Just to reiterate, partial charge is not a concern. AGM batteries charge slower than the old lead acid batteries, but they are much better at powering all the electronics in modern cars. The main reason you see the battery charge drop is because these cars don't fully turn off. They are like a cellphone in some ways. The connection to the Internet and telematics stays alive, so that you can remote lock/unlock/start and check on the status of the car. That's where the standby mode comes in. It doesn't hurt to periodically fully charge the battery if it has sat for a couple of weeks, but not when it goes to fully charged from normal driving and then just drops back down to partially charged.
Thanks, so it sounds like a 12v AGM. Any idea where this sits in a 2020 GLC?
Should be driver side under the plastic cowling in the engine bay. On some vehicles it can also be under the trunk floor.
Ah yes, looked there but it's the 48v lithium battery.
So either that lithium battery is a 48v and 12v combined, or it has a 12v sat in the boot as well, will take a look on the weekend.
Ah yes, looked there but it's the 48v lithium battery.
So either that lithium battery is a 48v and 12v combined, or it has a 12v sat in the boot as well, will take a look on the weekend.
Yeah, so in case of EQ Boost it could be that the 12 V battery is also a lithium battery. Have to make sure you use the correct charger.
This is a good place to find the correct charger. The OE charger is made by CTEK, but you can buy the same chargers for cheaper w/o the logo.
Indeed and that's kind of the question, what is that 12v battery i.e AGM or lithium as my Noco Genius 5 can do both but I need the right setting. If I could find the 12v (assuming separate from the 48v) then I could check the spec directly.
Indeed and that's kind of the question, what is that 12v battery i.e AGM or lithium as my Noco Genius 5 can do both but I need the right setting. If I could find the 12v (assuming separate from the 48v) then I could check the spec directly.
I am awaiting a call back from Mercedes, as they seem to be the only ones that know anything about this system. Even a very well known local specialist didn't have a clue.... as even though I have now worked out all the below, I still don't have 100% confirmation you can use the jump ports to directly charge the 12v battery (albeit quite likely).
I have uncovered the clue as to where the batteries are though and a little more about it.
On a EU 2020 GLC300, there are categorically two batteries. A 48v lithium ion battery that sits in the space where a traditional 12v would normally sit (under the plastic covers near the jump points), but there is also a 12v AGM sat in the boot floor.
The Mercedes technical documents say that you cannot charge the 48v directly, so I suspect that when you connect to the jump points it goes through a control box sat on top of the 48v, that directs the flow to the 12v in the boot floor and then it uses that to send converted current between the 48v and 12v.
Another good test for anyone else reading this in future months/years, a really easy way (wish I knew...) to check is the QR code that sits in fuel flap or drivers door sticker. This is meant for emergency services to see where battery/fuel lines are.
I believe those are in the owner's manual as well. Also the charging instructions, and charge points.
No you can't charge the 48 volt battery directly. A 12 volt charger hooked to the charge points (jump points) charges the 48 volt fire a DC to DC converter.
In that case it's a 12 volt to 48 volt converter, and the 12 volt is charged from the 48 volt system with the onboard 48 volt to 12 volt converter.
I believe those are in the owner's manual as well. Also the charging instructions, and charge points.
No you can't charge the 48 volt battery directly. A 12 volt charger hooked to the charge points (jump points) charges the 48 volt fire a DC to DC converter.
In that case it's a 12 volt to 48 volt converter, and the 12 volt is charged from the 48 volt system with the onboard 48 volt to 12 volt converter.
Thanks but a little confused
So, the 48 volt charges the 12 volt but you charge the 48 volt indirectly somehow via a dc to dc convertor that sits in the middle?
What charge mode (AGM/lithium) are you supposed to use to charge on the jump point and what does that actually directly charge ? As I guess there is a Battery management system to protect the 48v in any case.
Thanks but a little confused
So, the 48 volt charges the 12 volt but you charge the 48 volt indirectly somehow via a dc to dc convertor that sits in the middle?........
There is a DC to DC converter in each direction.
Applying your 12 volt charger to the 12 volt connectors under hood, will charge your 48 volt battery.
It's a good thing that that's there, because most people don't have 48 volt chargers.
(I'm talking about my GLE, so this might be an exact translation, but the principles are the same.)
There is a DC to DC converter in each direction.
Applying your 12 volt charger to the 12 volt connectors under hood, will charge your 48 volt battery.
It's a good thing that that's there, because most people don't have 48 volt chargers.
(I'm talking about my GLE, so this might be an exact translation, but the principles are the same.)
That makes sense and aligns with what I thought may happen.
The manual simply say those are the charging points but doesn't stipulate to which part of the system, at what voltage or with with what kind of charger.
So it sounds like 12 volt AGM charger on those connectors should be absolutely fine. Who would think charging a car battery would take so long to work out
Hello, I have a similar issue with my 2024 GLC 300. It has the 48 lithium ion battery in the front and the 12 volt battery in the boot.
I have been experiencing the same issues where the car leaves me stranded without being able to start. I received multiple warning messages of every system in the car. Pretty much coming on. And one time I had to have a towed to the dealership. This car is a 2024 with 900 mi on it. Brand new.!
I just went on a 60 mi drive round trip Christmas Eve, and today Christmas Day the car would not start with the same problems, all the warning lights coming on. On also my Mercedes app says that my 12 volt is critically low.
Not sure what's going on. I did take a voltmeter to the 12 volt battery and it does show over 12 volts. But the amperage could be bad as well. I just do not know. I would have assumed the dealership would have checked that on my first visit for this problem. Have you heard anything about this or have seen this issue ? You in advance for any info on this. I am taking the car into the dealership tomorrow morning. I have pretty much lost faith in any reliability on this car now and I am very shy of taking it on any distant drives.
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. My charger automatically detects the battery type, but yes it switches to AGM mode. Most Mercedes have an AGM 12V battery now and a few have lithium batteries, which requires a charger that supports lithium batteries.
