Dead battery

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Additionally my understanding is a normal charger will never be able to charge an AGM battery to its full capacity, I believe this is due to the higher voltage and AGM type battery is charged at.
My advice listen to MB if they state AGM then fit an AGM, If Lead Acid then a Lead Acid, and if required make sure you're charger will specifically charge an AGM
You will not have a problem charging your AGM battery with a modern smart charger, they are only trickle chargers and will not overcharge.
 
Evening all, I was playing with my new E55 this morning and thought I would try and use the feature for testing battery before startup and alternator health once started, unfortunately battery reading 11.6v and car turned over but failed to start. I've taken main battery out (mercedes/varta) out and charged up to 12.6v I will leave over night without charging, it does seem to be losing charge already (down to 12v in 1hr) so I'm assuming it's the main battery. My question to all is I've got a yuasa 100ah 900a wet battery that's in my Audi RS6 C5 ( selling after chrimbo to pay for new ride) which is only 3 yrs old, can I use that battery short term to check if the battery is the cause and until I can get the correct battery from mercedes. The only other cause I can think of is that the boot catch was stuck up, so maybe car thought boot was open (sedan) and the lights have stayed on and drained battery. From what I can see the battery manufacturer date is 2014 from what I can see, but I'm not 100% on that. Luckily I have the day off tomorrow but need to sort ASAP, so would really appreciate anybody's help, thanks.
Hi Matt
I've never owned a car with a two battery system but I believe that if you have a smaller battery in the engine compartment and a larger capacity one in the rear of the car, it is the smaller one that powers the starter.
If that is how your car is designed, the idea is that the starter battery can supply the very high current for the starter motor for a short period and the other battery is the general supply battery which is designed to provide lower current levels but can supply parking lights, hazard warning lights and all the modules without the alternator running and without the voltage dropping too low.
You said the engine turned over but failed to start. The two battery system means the cranking load doesn't drop the voltage of the engine electronics while you're trying to start the car but perhaps it was cranking too slowly.
I think you should thoroughly charge both batteries in turn.
I tried googling your charger but didn't get very far. I think it has a float mode, so ideally charge each battery until the charger switches to float mode which means it is taking a low current at the charging voltage limit. Then do the same with the other battery and if they were discharged from lack of use or short journeys and high winter loads you should be fine.
Do you have a voltmeter or a multimeter?
 
Hi Matt
I've never owned a car with a two battery system but I believe that if you have a smaller battery in the engine compartment and a larger capacity one in the rear of the car, it is the smaller one that powers the starter.
If that is how your car is designed, the idea is that the starter battery can supply the very high current for the starter motor for a short period and the other battery is the general supply battery which is designed to provide lower current levels but can supply parking lights, hazard warning lights and all the modules without the alternator running and without the voltage dropping too low.
You said the engine turned over but failed to start. The two battery system means the cranking load doesn't drop the voltage of the engine electronics while you're trying to start the car but perhaps it was cranking too slowly.
I think you should thoroughly charge both batteries in turn.
I tried googling your charger but didn't get very far. I think it has a float mode, so ideally charge each battery until the charger switches to float mode which means it is taking a low current at the charging voltage limit. Then do the same with the other battery and if they were discharged from lack of use or short journeys and high winter loads you should be fine.
Do you have a voltmeter or a multimeter?
Oh, and you won't harm an AGM battery using a conventional charger, limited to 14.4v.
 
Hi Matt
I've never owned a car with a two battery system but I believe that if you have a smaller battery in the engine compartment and a larger capacity one in the rear of the car, it is the smaller one that powers the starter.
If that is how your car is designed, the idea is that the starter battery can supply the very high current for the starter motor for a short period and the other battery is the general supply battery which is designed to provide lower current levels but can supply parking lights, hazard warning lights and all the modules without the alternator running and without the voltage dropping too low.
You said the engine turned over but failed to start. The two battery system means the cranking load doesn't drop the voltage of the engine electronics while you're trying to start the car but perhaps it was cranking too slowly.
I think you should thoroughly charge both batteries in turn.
I tried googling your charger but didn't get very far. I think it has a float mode, so ideally charge each battery until the charger switches to float mode which means it is taking a low current at the charging voltage limit. Then do the same with the other battery and if they were discharged from lack of use or short journeys and high winter loads you should be fine.
Do you have a voltmeter or a multimeter?
The second battery in the case of a 211 and 219 is purely for the SBC Brake system.
All car functions are normally run from the Main rear Battery.
 
My advice listen to MB if they state AGM then fit an AGM, If Lead Acid then a Lead Acid, and if required make sure you're charger will specifically charge an AGM

I'd agree with this as the charging system voltage will have been calibrated to suit the type of battery.

Your experience with an AGM is not typical. An AGM should have a lower internal self discharge rate than a standard battery because the internal resistance is lower. Compared to what was once the basic standard wet cell battery, an AGM should hold it's charge very much longer. The difference being huge in my experience. That said standard batteries are not really standard these days. The typical "standard" automotive OEM battery has been improved with a lower internal self discharge rate than they used to have. An AGM should still be better though.

The only difference in battery types is in the construction. Varta for example make a least 3 different battery types: Standard Enhanced and AGM but they are all lead acid.
 
The second battery in the case of a 211 and 219 is purely for the SBC Brake system.
All car functions are normally run from the Main rear Battery.
OK, thanks. So Matt only needs to give the rear battery a full charge to solve his starting problem, assuming of course that the battery is in good condition and is just in a low state of charge....
 
OK, thanks. So Matt only needs to give the rear battery a full charge to solve his starting problem, assuming of course that the battery is in good condition and is just in a low state of charge....
That is correct
 
Just replaced the battery from the dealer, gave me a nice discount and was cheaper than any I've seen online, went to start car and loads of cranking power but no start, any ideas anyone, checked what fuses I could but feeling a little on the browned off side so having a brew, I'll prob end up calling RAC, car was running fine before, could it be immobilizer or something I have to reset? Thanks everyone.
 
Thanks, what is the spec on your yuasa battery? Same as original? Cheers Matt.
Better. 95ah and 850CCA Yuasa YBX9019 AGM Stop - Start.
No need to calibrate. Out with the old and in with the new. 10mins
 
Good news, I read somewhere that if you point the key at the base of the rear view mirror and give key a few clicks, I also read try starting the car in neutral, anyway car fired up straight away, not sure how or which one of the two did the trick so I'm more than happy, alternator reads 14.2 when engine running and car solid on test drive, seem to have lost interior reading lights and headlights don't stay on for short period when car is locked but I can sort that. All in all an emotional morning, horrible when there is something amiss with the old pride and joy, thanks for all help and advise given, and a big thank you to Dave the parts guru at Taunton mercedes for sorting me out a real good deal in a oem AGM battery which they had on the shelf.
 
Hi Matt
I've never owned a car with a two battery system but I believe that if you have a smaller battery in the engine compartment and a larger capacity one in the rear of the car, it is the smaller one that powers the starter.
If that is how your car is designed, the idea is that the starter battery can supply the very high current for the starter motor for a short period and the other battery is the general supply battery which is designed to provide lower current levels but can supply parking lights, hazard warning lights and all the modules without the alternator running and without the voltage dropping too low.
You said the engine turned over but failed to start. The two battery system means the cranking load doesn't drop the voltage of the engine electronics while you're trying to start the car but perhaps it was cranking too slowly.
I think you should thoroughly charge both batteries in turn.
I tried googling your charger but didn't get very far. I think it has a float mode, so ideally charge each battery until the charger switches to float mode which means it is taking a low current at the charging voltage limit. Then do the same with the other battery and if they were discharged from lack of use or short journeys and high winter loads you should be fine.
Do you have a voltmeter or a multimeter?
Thanks for your advice, bought a new battery from dealer in the end, after sorting some reset gremlins the car fired up lovely, what a relief.
 
I had a good result the other week. I've not long since bought a 2013 SL350 and found the battery to be original. So I did all the normal checks and found that the battery was getting a bit tired, although it was starting the car ok. Anyway when I bought the car it came with a six month warranty with a well known company which covers the battery. To cut a long story short they paid out for a new battery no questions asked. :banana:
 
Good news, I read somewhere that if you point the key at the base of the rear view mirror and give key a few clicks, I also read try starting the car in neutral, anyway car fired up straight away, not sure how or which one of the two did the trick so I'm more than happy, alternator reads 14.2 when engine running and car solid on test drive, seem to have lost interior reading lights and headlights don't stay on for short period when car is locked but I can sort that. All in all an emotional morning, horrible when there is something amiss with the old pride and joy, thanks for all help and advise given, and a big thank you to Dave the parts guru at Taunton mercedes for sorting me out a real good deal in a oem AGM battery which they had on the shelf.
I had a very similar experience...I have an E55 too.
My battery was dying/dead and I as a result had the big red battery sign on the dash.
I tried charging etc but it couldn't hold enough charge, so I did the same as Matt and bought one from the main dealer. The price was equal to online and the dealer is 10 minutes up the road and so within 30 minutes it was installed in the car and all my issues (battery wise anyway) were solved.
 
What would be the result if a non AGM battery was fitted by mistake.
 
What would be the result if a non AGM battery was fitted by mistake.
Probably nothing if the start/stop was turned off, as most people do.
 
I wouldn't mind betting your memory seat modules are causing a parasitic current draw and draining the battery. It seems to be a very common problem with the w211 and and thankfully an easy fix.
 

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