How to charge/find 12v battery in GLC300 EQBoost 48v?

[v6matt]

Hi All, I have a new to me 2020 GLC300 mild hybrid.

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 or jump the 12v (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?

Thanks

 

[Headhurts]

I have a 2021 GLC300 that had only completed 2300 miles when I purchased it 2 1/2 months ago, I had to travel to Blackburn from Norfolk to collect it which is a trip of around 5 hours.

I was getting the occasional warning about low battery voltage so I put it on charge using the connections under the bonnet a couple of times using my CTEK MXS5.0 charger but I still received the occasional low charge warning, I was resolved to having a new battery.

I decided to try once more to charge the battery but selected AGM recondition mode, I have not had any problems since running a recondition cycle.

I’m not sure if this would be useful to you?

Like a few Mercedes they do seem to need a full charge to prevent issues.

Robin

 

[Benz17]

Hi All, I have a new to me 2020 GLC300 mild hybrid.

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 or jump the 12v (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?

Thanks

Would the battery deteriorate in 2 year’s.

Have you tried charging it first, and then see how it goes.

On my 2017 W213, it also shows partially charged in MM if it hasn’t been driven for a few days, once driven it shows fully charged. Granted mine is not a mild hybrid.

 

[v6matt]

I have a 2021 GLC300 that had only completed 2300 miles when I purchased it 2 1/2 months ago, I had to travel to Blackburn from Norfolk to collect it which is a trip of around 5 hours.

I was getting the occasional warning about low battery voltage so I put it on charge using the connections under the bonnet a couple of times using my CTEK MXS5.0 charger but I still received the occasional low charge warning, I was resolved to having a new battery.

I decided to try once more to charge the battery but selected AGM recondition mode, I have not had any problems since running a recondition cycle.

I’m not sure if this would be useful to you?

Like a few Mercedes they do seem to need a full charge to prevent issues.

Robin

Thank you Robin, this is very helpful.

So certainly sounds like there is a 12v AGM hiding somewhere. Did you ever find it? Or just used the jump connectors under the bonnet ?

 

[v6matt]

Would the battery deteriorate in 2 year’s.

Have you tried charging it first, and then see how it goes.

On my 2017 W213, it also shows partially charged in MM if it hasn’t been driven for a few days, once driven it shows fully charged. Granted mine is not a mild hybrid.

I dont think it would, I suspect it was just sitting for a while before I bought it.

I am thinking it's discharged somewhat that it's best to fully charge it but the question of this thread really is how you charge this eqboost system as it's got both a 12v and 48v system with presumably two different batteries. However it does seem the battery on the jump leads is an AGM 12v of some flavour.

 

[SL63 Mark]

Surely the 48V system would charge up the 12V ? A 48V battery is simply four 12V batteries in parallel.

Just thinking aloud, I am completely ignorant about mild hybrids, but do understand a tiny bit about volts.

Are you experiencing any symptoms ? If not, I would leave well alone. You can cause more harm than good by randomly attaching battery chargers.

 

[EmilysDad]

Surely the 48V system would charge up the 12V ? A 48V battery is simply four 12V batteries in parallel.

Just thinking aloud, I am completely ignorant about mild hybrids, but do understand a tiny bit about volts.

Are you experiencing any symptoms ? If not, I would leave well alone. You can cause more harm than good by randomly attaching battery chargers.

series

 

[Wearsafoxhat]

series

was just about to say the same…


Sent from my iPad using Tapatalk

 

[v6matt]

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.

This is the link it sends me to, you can clearly see both the batteries https://rk.mb-qr.com/en/253.9/

 

[Srdl]

but the question of this thread really is how you charge this eqboost system as it's got both a 12v and 48v system with presumably two different batteries.

i think the lack of any response shows that none of us on here have any clue either because it’s such a new system.

 

[Headhurts]

Thank you Robin, this is very helpful.

So certainly sounds like there is a 12v AGM hiding somewhere. Did you ever find it? Or just used the jump connectors under the bonnet ?

I used the connections under the bonnet, slide back the red cover on right as looking from the front to reveal the positive connector and nearby is a brass looking post to connect the negative terminal.

It did take around a day to recondition but since then I have not had an issue.

I am not sure exactly where the 12v battery is but thought it to be in rear under floor trim.

Robin