SL 350 Auxiliary battery 2014

2014Merc350SL

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Hi. Can anyone tell me where my Auxiliary Battery is on my SL 350 2014 (UK) model please? Col.
 

ToeKnee

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Behind the drivers seat. Move the seat forward, grip the bottom of the panel and pull upwards and outwards, then the top panel will come off and the battery is just visible beneath a plastic cafe route cover
 

ToeKnee

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Last sentence should say "visible beneath a plastic cage type cover", sorry autocorrect.....
 
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2014Merc350SL

2014Merc350SL

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Thanks agin - I probably asked the wrong question - my problem is my consumer battery is "flat" or low and I want to charge it or fit a maintainer - or connect it to a maintainer ...I have found the consumer battery (thanks for your help) but it looks like it has a live and earth wire not a live a neutral - I have now read you charge the consumer battery near the starter battery - and connect the neutral to the starter battery !
The starter battery its not under the bonnet as most videos on the net shows - so I guess my question is how do I charge the consumer battery and if that involves finding the starter battery - where is that on an 2014 SL 350 UK model ...hope this makes sense to someone :) col. thanks for any help
 

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There should not be a neutral wire on a car battery, only positive and negative. The main battery is in the boot under the parts tray. Remove the flat board in the boot and you'll find the shaped tray that holds the the compressor etc, empty that tray and remove and you'll see the battery. I, and others, charge this battery direct straight to the terminals but you can charge it to the battery terminals under the bonnet. The battery behind the drivers seat is the auxiliary battery.
 
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2014Merc350SL

2014Merc350SL

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Thx - I am retired gas fitter ...I meant negative but old habits. Its the auxiliary I need to charge not the car main battery. This looks like it has a positive and a wire straight to the car body
 

ToeKnee

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Most modern cars are negative earth so the wire from the negative post would go to the chassis. To charge simply put the battery charger positive on the battery positive post and the negative from charger either on the negative post or straight to the chassis, job done.
 
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2014Merc350SL

2014Merc350SL

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Most modern cars are negative earth so the wire from the negative post would go to the chassis. To charge simply put the battery charger positive on the battery positive post and the negative from charger either on the negative post or straight to the chassis, job done.
Thanks agin
 

Rorywquin

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Thx - I am retired gas fitter ...I meant negative but old habits. Its the auxiliary I need to charge not the car main battery. This looks like it has a positive and a wire straight to the car body
Aren’t there charging posts under the bonnet? In my car and I’ve been using them for 5 years (17,000 miles) without an issues keeping both charged. The car stands for long periods on the charger not being used. Pretty sure your car is the same. MAKE SURE YOU CHECK YOUR BATTERY TYPE _ PROBABLY AGM AND YOUR CHARGER SHOULD BE SET TO AGM MODE IF IT IS. Screenshot 2022-01-18 at 09.04.20.png
 

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There should be battery posts under the bonnet as mentioned in post#6 which can be used successfully to charge the main battery. I've found it easier to go direct to the battery in the boot but your circumstances may be different to mine.
 

Rorywquin

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There should be battery posts under the bonnet as mentioned in post#6 which can be used successfully to charge the main battery. I've found it easier to go direct to the battery in the boot but your circumstances may be different to mine.
I find it easier to open the bonnet and connect to the posts provided for the purpose rather than :

"Remove the flat board in the boot and you'll find the shaped tray that holds the the compressor etc, empty that tray and remove and you'll see the battery.....":)

I don’t see any reason to do it differently to what MB recommend in the owners manual, but each to their own.

From my experience, the AUX also gets charged from the jumper posts i.e. if I leave the car on the charger, the ECO light is always green when I use the car inspite of short trips / infrequent use. Why would MB make this a complicated process for a luxury car which most people wil use as a “fair weather” ride.
 
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ToeKnee

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Hi Rory, I've got a permanent ctek connector to the rear battery so it's very easy to connect plus my mains plug is closer to the boot. My eco light is also always green after charging straight to the battery. As for your quoted part of my post, that was more so the op knew where to find the battery rather than an instruction to only charge the battery from there. 👍
 

Rorywquin

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............... My eco light is also always green after charging straight to the battery. .........


What you say supports my experience that there is no need to separately charge the aux. On one of the USA sites, they seem to have a thing for connecting pigtails to the aux and charging it separately.

I expected that you may have a reason for charging at the boot.
 

Toffee

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Hi Guys - looks like my auxiliary battery is ...busted. It wont hold a charge and some things are not working such as: auto engine switch off and start when stopped at traffic lights. Ok..thanks to your help I know were it is and have tried to charge it. I am now thinking of replacing - i want to ask is this a simple task of buying a replacement (somewhere) removing it and replacing it - like for like - remembering to disconnect the main battery. Anyone got a recommendation what to replace it with. 2014 SL 350 (uk) model (September 2014) any other safety advice. all help very welcome - Col.
 

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