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My understanding is the GLC doesn鈥檛 have a separate Starter Battery 馃

Forum member Toobad tracked the Stop / Start functionality to a large capacitor unit that sits under the passenger footwell.

When we purchased the car a salesman said there was an auxiliary starter battery under the passenger seat - Not True
 

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Hi, I'm getting mid 30's urban, and 40+ Dual Carriageway (no motorways up here). I would sit in with them on the test run, with everything zeroed at get go. As for the Battery, it's a 'Gas Mat' type, designed for the 'Stop/Start' system, with rapid voltage recovery. A low voltage would negate S/S system, as do some other parameters. Please tell me you don't have Sport mode selected, ie you're in 'Comfort'. Next step would then have to be an independent test (RAC/AA). You can also connect a 'Bluetooth transmitter to your OBD Port and send the readings to your Phone or Laptop.. Good Luck.
 

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Discussion Starter · #23 ·
Hi guys,

They told me it was the starter battery that was replaced, however im assuming that's the auxiliary battery as it was for a stop/start fault?

Had the car away a big trip of around 550 miles and I got 37mpg with an average speed of 57mph, I would say it was 90 percent motorway and was sat between 70 and 80 all the way.

Regarding driving mode its always in eco/comfort as im horrified to see what the fuel would be like if I had in in sport and throttling it everywhere 馃槀

The car then came up saying auxillary battery fault on the dash in red when I was about half an hour from home.. It soon changed to white but is there permanent now. Have contacted the dealership and they are straight away trying to say its a different fault from the battery they replaced.. Again 4/5 days after that replacement battery it needed charged again and now ive got this other so called new fault.. All seems a bit suspect to me and they just seem to be trying to dodge actually fixing the problem.

Car going back in on Thursday morning so will update once I get fed more Bull**** from them 馃槱
 

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2016, GLC250D 4 Matic AMG Sport Premium
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Hi, there's only one battery fitted, and that is under bonnet. Technically speaking it IS the Starter battery. The normal 'stealer' battery diagnosis is to fully discharge the existing battery, fully recharge it and monitor the charge over 24 hours or so. If the battery fails test they replace it, that's why it takes so long. Get them to test out the Alternator, as if this has a problem it could be sucking so much power to turn it, that it would affect your mpg. Good Luck.
 

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Discussion Starter · #25 ·
Hi, there's only one battery fitted, and that is under bonnet. Technically speaking it IS the Starter battery. The normal 'stealer' battery diagnosis is to fully discharge the existing battery, fully recharge it and monitor the charge over 24 hours or so. If the battery fails test they replace it, that's why it takes so long. Get them to test out the Alternator, as if this has a problem it could be sucking so much power to turn it, that it would affect your mpg. Good Luck.

Hiya mate, so got the car back after replacing the auxiliary battery and seems to all be resolved for time being. Seem to be getting better readings on fuel also now. Think they checked the alternator when it was in, however if I continue to have problems with the batteries then its pointing towards that.. I will just needto see how it is over the coming months 馃憤馃徎
 

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Hi Chris, thought it was worth replying to this thread in case you havent got to the bottom of your fuel consumption problems.

My wife had an e class coupe with the same 250d engine and similar poor economy figures.
The air filter element is on a stupidly long interval for changing and after replacement it was like night and day.
After 25k miles it was still the factory filter and was proper filthy. After changing we improved around 8-10mpg and the extra throttle response was noticable.
You found yourself backing off the throttle far more because of the extra response.

I think the filter was under 20 quid and easy to change. It's on the top of the engine.
You may have changed it already but if not it's worth a go

Good luck
Mart
 

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Hi Guys,

Ive just recently purchased my GLC and it has been nothing short of horrendous on fuel. We get around 17/18mpg around town and struggle to get 33/34 on a longer run.. I got around 290 miles to a full tank of diesel and that was driving it very sensibly.. Horrified to think what it will be down to when giving it a hard time 馃槀

Any help with this would be much appreciated.

Cheers
What mode are you in SPORT / SPORT+ or comfort as I have noticed a difference in economy on my GLC350D however i do fare better with your figures, even when toewing a 1700kg caravan I still get 24 mpg
 

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Hi All, I've been through the WIS System and just to confirm, there is only ONE battery. It's classed as the LISB (Lithium Iron Starter Battery). It's the normal Battery in the Rear Left of the engine bay.
 

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My understanding is The Auxiliary Battery is a Capacitor that鈥檚 used to power the Auto-Restart - it鈥檚 not a 鈥榬eal鈥 battery. This unit is located in the passenger side footwell
 
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