Auxiliary Battery Malfunction
Thread Starter
Senior Member
Joined: May 2016
Posts: 379
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From: ALLENTOWN PA
2017 AMG GT, 2015 ML350, 2013 C300
Auxiliary Battery Malfunction
I rarely use my 2015 ML. There was a stretch of 2 months that I did not even start it. After I finally did, I got the "Auxiliary Battery Malfunction" message. I thought this would go away after driving for a while. Not so.
Is this the main battery or one of those tiny "backup" battery that I need to replace? Is there a reset procedure just to see if this really need replacing?
Thanks in advance.
Is this the main battery or one of those tiny "backup" battery that I need to replace? Is there a reset procedure just to see if this really need replacing?
Thanks in advance.
Member
Joined: Aug 2016
Posts: 125
Likes: 23
From: Huntsville, AL
2014 ML63 AMG
I rarely use my 2015 ML. There was a stretch of 2 months that I did not even start it. After I finally did, I got the "Auxiliary Battery Malfunction" message. I thought this would go away after driving for a while. Not so.
Is this the main battery or one of those tiny "backup" battery that I need to replace? Is there a reset procedure just to see if this really need replacing?
Thanks in advance.
Is this the main battery or one of those tiny "backup" battery that I need to replace? Is there a reset procedure just to see if this really need replacing?
Thanks in advance.
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Joined: Mar 2004
Posts: 1,175
Likes: 24
From: Boston, MA
'14 ML350, '13 C220 CDI, '07 C280, '98 ML320
Depends on how much time you got on your hands :-)
You can remove the battery and trickle-charge it and see if the problem goes away. If the problem doesn't go away afterwards, you may need to replace it.
Since it is tucked behind the main battery (at least on my truck, it is), and it is not that easily accessible, if I were you, I'd replace it with a new one and be done with it.
You can remove the battery and trickle-charge it and see if the problem goes away. If the problem doesn't go away afterwards, you may need to replace it.
Since it is tucked behind the main battery (at least on my truck, it is), and it is not that easily accessible, if I were you, I'd replace it with a new one and be done with it.
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From: The Great White North
W204 C63 Coupe, W166 ML350 BlueTEC, 928GT, Taycan GTS Sport Turismo, C5 Z06 & IS300 race cars
The aux battery on every W166 I've ever seen is located behind the right side rear panel in the cargo compartment (below the spare near the tail light). It's a SLA unit so I certainly would NOT attempt to trickle charge it, and at ~$50 it makes a lot more sense to just replace it with a new one.
Senior Member
Joined: Sep 2012
Posts: 323
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From: Ottawa ON Canada
2015 ML350 Bluetec
The aux battery on every W166 I've ever seen is located behind the right side rear panel in the cargo compartment (below the spare near the tail light). It's a SLA unit so I certainly would NOT attempt to trickle charge it, and at ~$50 it makes a lot more sense to just replace it with a new one.
Thread Starter
Senior Member
Joined: May 2016
Posts: 379
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From: ALLENTOWN PA
2017 AMG GT, 2015 ML350, 2013 C300
I haven't look in the rear panel area but I did open the floor panel under the rear passenger seat and there is, what looks to be a fuse box there.
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From: The Great White North
W204 C63 Coupe, W166 ML350 BlueTEC, 928GT, Taycan GTS Sport Turismo, C5 Z06 & IS300 race cars
Hmm... not sure, but in my 2015 ml350bt the aux?? battery in underneath the right passenger rear seat. Just flip seat base and remove cover.... or is this the main battery? I may be wrong, having not any need to search, but I believe the main battery is located in the engine bay compartment, buried in the right(passenger) side near shock?
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From: The Great White North
W204 C63 Coupe, W166 ML350 BlueTEC, 928GT, Taycan GTS Sport Turismo, C5 Z06 & IS300 race cars
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Senior Member
Joined: Sep 2012
Posts: 323
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From: Ottawa ON Canada
2015 ML350 Bluetec
You're right... fuse box under rear passenger seat. I was trying to remember why I thought that, and it was when I hooked up my trailer lights +power for the trailer module! sorry, good luck
Member
Joined: Aug 2016
Posts: 125
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From: Huntsville, AL
2014 ML63 AMG
The aux battery on every W166 I've ever seen is located behind the right side rear panel in the cargo compartment (below the spare near the tail light). It's a SLA unit so I certainly would NOT attempt to trickle charge it, and at ~$50 it makes a lot more sense to just replace it with a new one.
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Joined: Jan 2013
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From: The Great White North
W204 C63 Coupe, W166 ML350 BlueTEC, 928GT, Taycan GTS Sport Turismo, C5 Z06 & IS300 race cars
They are rechargeable batteries so obviously there's nothing wrong with recharging them - for as long as it's done with a charger that has very good voltage regulation, which is not the case with 99% of all automotive battery chargers (trickle or otherwise). Poor voltage regulation results in overcharging and thus excessive formation of hydrogen gas, which - unlike in a wet cell battery which is always vented - in a SLA battery has nowhere to go and results in internal battery damage.
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Joined: Mar 2004
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From: Boston, MA
'14 ML350, '13 C220 CDI, '07 C280, '98 ML320
They are rechargeable batteries so obviously there's nothing wrong with recharging them - for as long as it's done with a charger that has very good voltage regulation, which is not the case with 99% of all automotive battery chargers (trickle or otherwise). Poor voltage regulation results in overcharging and thus excessive formation of hydrogen gas, which - unlike in a wet cell battery which is always vented - in a SLA battery has nowhere to go and results in internal battery damage.
^ +1.
Thread Starter
Senior Member
Joined: May 2016
Posts: 379
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From: ALLENTOWN PA
2017 AMG GT, 2015 ML350, 2013 C300
If this is the one, how the hell do you get this out? lol 95% of it is under the carpet. Do I need to gut the trunk out to get to remove it?
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From: The Great White North
W204 C63 Coupe, W166 ML350 BlueTEC, 928GT, Taycan GTS Sport Turismo, C5 Z06 & IS300 race cars
Yes, that's the one. You need to take out the side panel. There are a couple of plastic "hooks" with a Torx screw in the middle - you need to take those out and then you can remove the panel.
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Joined: May 2017
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From: Long Island, NY
2014 ML350 4MATIC
You can remove/re-install the small aux battery without cutting the carpet, and without removing the entire passenger side trunk liner (panel).
I just did it.
Wasn’t easy, but it’s possible.
I didn’t want to remove side trunk side panel, because I didn’t want to pull off the trunk’s rubber seal.
I just did it.
Wasn’t easy, but it’s possible.
I didn’t want to remove side trunk side panel, because I didn’t want to pull off the trunk’s rubber seal.
