phbalance724

3 weeks ago I just bought my '06 SL500 with 34,500 miles on it. Today, after putting a total of only 500 miles since buying it the battery is completely dead and car wont start. I live in two different cities and can only drive the car on the weekends. I've done some searches and learned all these different components that could be draining the battery. I went to two places (Sears and NTB) to try to get it replaced and neither one had it in stock bc they said it was a smaller than normal battery.

A lot of you guys seem very car savvy and know how to diagnose and fix any problem...I am not one of those guys
So plz bear with me on some of these questions...

1. should i get the battery at a MB dealer or will an aftermarket battery suffice? I know MB will be more $$$.

2. Is it just me, or does it seem ridiculous to try to self-diagnose what could be draining the battery (if indeed there was something draining it) on a $50K vehicle? I'm reading some ppl are ejecting navi discs, removing fuses, sitting in their cars for 30 mins after shutting it off and doing all sorts of other things in which I have no idea what they're talking about.

3. After reading my manual, I still am not sure what the battery in trunk is for - it states for electrical consumers? Does that need to be replaced as well?

Thanks for any help!

jajara

i have the same thing happened to me have them check voltage regulator it is a 49 $ part plus the trunk battery is 300 bucks... good luck friend

velvet fog

The small battery under the hood is for starting the car, the trunk battery powers most everything else. Usually if you get an electric problem (or leave your lights on) it drains the rear battery and your car still starts from the front battery. When the rear battery is drained, you get a message in the cluster saying electrical consumers offline (or something similar)

Your front battery could be just at the end of it's life although I'm still on my original front battery in my 2005. I'd try replacing the front battery first. Both batteries are odd sized, probably a dealer only item. When I tried to find a rear battery I couldn't find a non MB battery.

AMGfan

This problem (battery drain) hasn't really never been definitively diagnosed to my satisfaction (I've had numerous dead batteries on all the MB's I've owned). So, I've done the following:

1. Invest in a battery trickle charger. You can get one through MB but they will screw you on price. You can find one on Ebay for less than $120...you can check with MB and I bet it is at least twice as much.

Just keep it connected while you are gone and it should do fine.

2. I've always bypassed MB with regards to replacing a battery. They screw you on the battery price and install charge. If you are really aversed to replacing the battery yourself then at least take it to a MB indie...you can at least save money on the labor.

Good luck.

Rook3300

Yes as AMGFan states, get a trickle charger for sure. You're not driving the car often enough to keep the battery charged properly so at the very least, you will shorten the life of it. It seems that the battery may be old and not keeping a charge for very long. There are electronics that require voltage whether or not there is a problem, so it could just be a bad battery. A trickle charger will fix that and keep a new battery in better condition over the long haul.

You can purchase the rear battery from an AutoZone or similar. It is huge and expensive (for a battery). The front battery is difficult to find (if at all). I had to purchase it from the dealer. Both batteries are easily changed even by someone with little experience. Seriously, just take your time and watch what you are doing -- it should be no problem.

-ROOK

NikleinR6

As others have stated, pick up a trickle charger. The CTEK 3300 is an excellent one, and is most likely the same charger that Mercedes will sell you (just with Mercedes on it instead of CTEK labeling). In fact, they look identical.
It is a well known fact that our cars will drain batteries if they are not driven often. For some reason, most European cars do. Some manufacturers, like Porsche, have taken steps to reduce the problem. On my 911 C4S, after a certain number of days have passed, and the car is not driven, a lot of the accessory options will shut themselves down, such as the remote functions, etc. I have to open the doors manually with the key, start the car, and then the remote functions will work again until the car sits again for a few days or so. In Mercedes, their solution to battery drain was "We'll just put 2 batteries in". The idea was that the front battery is only used to start the car. Therefore, it shouldn't drain in power because there are no accessories linked to it. Instead, it will only weaken with age. The rear battery has all of the accessories attached to it, so it will drain as the car sits. Mercedes was not concerned with this, because when it drains, the car will still start, and the driver may have to put a couple of miles on the car before the alternator has a chance to charge it up enough for the convenience options to function again. They believe this to be a good system. The only problem with this is that if the rear battery is severely discharged from sitting for a long period of time, it may cause it to lose/damage cells that won't return to full charge. Then you are looking at replacing a 240.00 battery. For this reason, I keep both my SL55 and also my 911 connected to CTEKs.

Furthermore, if you research other forums, you will find a lot of info on Mercedes batteries and electronics. I have read various threads where over and over again, it is stated that Mercedes batteries are intended to last around 5 years. After that, you should have it regularly checked, and replaced if necessary. I have read threads where people have had weak batteries and ruined their alternators from overworking them. It is cheap insurance for a 140.00 front/starter battery from Mercedes (240 for the rear, which seems to last much longer than the front, especially if connected to a trickle charger). Alternators can be very very expensive so at the 1st sign of battery failure, I would have it checked/monitored closely, and replaced very quickly.

I have also read in various places that Mercedes electronics are some of the most sensitive of any of the automakers. For that reason, I have gathered that it is not a good idea to replace these batteries with anything but OEM. I can't remember the figures exactly, but I think OEM batteries are 100AH or maybe 120AH, and most aftermarket are lower (please research as it has been a long time since I gathered this info, and I can't remember the exact figures). For this reason, people who have replaced their batteries with Wal-Mart or AutoZone batteries (rated at different AH) may find slight glitches in some of the electrical equipment such as alarm issues, cluster lights coming on, etc. This is an idea I am unwilling to entertain. I will only install OEM. Sure they are marked up in price, and higher than most others, but they are cheap insurance in the event that some electrical component fails. I would hate to have a warrantee claim denied on a failed component because of the use of an aftermarket battery.

SO, WHAT TO DO??
The best way to buy a Mercedes battery is to either
1) Go to the dealer, buy the battery, and spend 10 minutes max to install it with simple tools.
OR.
2) All Mercedes have free roadside assistance for life. If you call the dealer and have them send roadside assistance to your house to replace your battery, they will do so for only the cost of the battery, and labor will not be charged.
Either way, both options cost the same, just whether or not you feel like doing it yourself, or having someone else do it. DO NOT GO TO THE DEALER AND HAVE THEM REPLACE IT AS THEY WILL CHARGE YOU A 1 HOUR MIN TO INSTALL.

I hope all this info helps. I wish I could remember more of the specifics of a lot of research I had done earlier this year when I was having starter battery issues.
I replaced mine with OEM.

-Nick

NikleinR6

Here are some pics for reference. You can see why you should buy the CTEK 3300 for half the price of what Mercedes will sell you their charger for..
I am nearly positive they have CTEK make their chargers, and just badge them differently.

OEM..



CTEK

AMGfan

Nick...I've asked my MB parts guy and did confirm CTEK is mfg with no difference in internals. That MB branding (not to mention every other Euro brand) is a pretty penny.

On my E55 I actually have 2 CTEKs...one for the main and one for the smaller aux front battery. FOOTNOTE: The front aux battery is considered equivalent bike battery and the setting on the CTEK is set at that rating.

phbalance724

thanks for posting the pics Nick and all you guys suggestions. I just went to Sears but they did not have that CTEK charger so I will search some more.

So now that I've learn that the trunk battery is for all the other accessories, how will I know if it's ever low or dead? Will my radio or lights just stop working?

velvet fog

You will get the "electrical consumers offline" message in your instrument cluster.

FWIW, my car can sit for 2-3 weeks with no battery problems.

mkirincic

Both of the batteries are unique and have limited sources. The best solution is to register your car with Mercedes Benz for Road Side Assistance. then call roadside assistance, they will come out and install the battery for you. this is cheaper than going to the dealer for service. I had my starting battery replaced for $180 installed in my driveway vs. $330 if the car was brought to the dealership. The battery was from MB the same as if you were to bring your car into the dealership for service. Quick also, they showed up at my house within 30 minutes of my initial call.

phbalance724

So it is recommended I get two chargers so the one in my trunk doesnt drain out as well?

Got my car at BMW dealership, does any MB car qualify for roadside assistance?

NikleinR6

I have been told that one CTEK connected to the rear battery is all you need. I only use 1.

I have been told that for all MB owners, roadside service is free for life... Check into it. I think you will find it a convenient way to get your battery replaced quickly...

-Nick

phbalance724

Gotcha, but shouldnt it be connected to the front battery since that's the one responsible for starting the car?

NikleinR6

Well, like i said earlier, the front battery has no accessory options connected to it, so there is essentially no drain (at least there shouldn't be)... Therefore, the only thing that should weaken the front battery is age, at which point it should be replaced anyway. The rear battery is completely different. It does lose its charge fairly quickly...

If the car was going to sit for 3 or more weeks, maybe then i would hook up an additional CTEK to the front battery (if you really want to). Otherwise, just a CTEK hooked up to the rear battery should sufficiently protect and condition it. A healthy front battery shouldn't let you down until it becomes around 5 or so years old...

-Nick

jgoode

can anyone confirm if the front battery should be on a trickle charger?

04sl55mb

It looks like the charger can be hard wired to the battery and the charger stays in the trunk. Does they battery have to be momentarily disconnected while hard wiring the charger? If so does that have any effect on the electrical system?

rune solem

You don't need to trickle charge the front starter battery, because it's only used when you start the car.

So it doesn't loose it's charge like the battery in the trunk.

I have the car stored in the winter (in norway), so I just disconnect the rear battery, but a trickle charger is of course the best way to keep it in maximum health.

I think i also remember that I read somewhere, that when you charge up the rear battery in the trunk, you also charge up the front battery, but i'm not 100% if that's a fact, maybe someone else here knows for sure.

rleckhardt

Would you mind if I asked what the wheels are on your blue Mercedes in the picture? I have been looking all over for wheels like that. I have a 2007 SL550 in need of wheels.
Thanks,
Ray E.

rune solem

The rims I have are discontinued ANTERA rims.

Here's their web adress: http://www.antera.it/

Maybe they have some newer you would like instead?

If not, you will have to buy a used set somewhere.

Tahoe SL

Hi all, is there any reason why a Battery Tender product wont work ? I used one on my ZR1 Corvette for years and it worked fine.


Dave

fixitguy63

I have one the battery goes down overnight or all day sitting. the customer just put a new battery in it. I checked it for a draw and I don't have one at this moment. the amp draw was .05 amps.