spinn

The starter solenoid is what completes the circuit between the battery and starter. If you don't jump start at the rear battery, how does it complete the circuit if the solenoid is not connected to the aux battery?

spinn

p. 378 of my 04 E500 owner's manual states: "Jump starting may only be performed on the main battery in the trunk."

p. 379 shows the connection of the jumper cables to the rear battery.

I don't know what system you're talking about...

notten

The aux battery under the hood is a backup for the SBC (braking) system in our cars. It is NOT to be used to jump start the car. Do you really think that MB would put the jump start battery under an air filter only accessible by removing a nut? Nope. The correct jump point is most certainly in the trunk. There is also a jump point under the hood, but this is NOT the usual place. The correct place to have your car jump-started is in the trunk. I have had MB come by and give me a boost after letting her sit for some time, and they did it from the trunk. The trunk battery is used for EVERYTHING in the car. The hood battery is for the SBC system backup battery only.

Plutoe

I admit that the information I posted was incorrect for this model.I have removed all my comments.


however please note that there are models(not W211) that use a conventional lead acid battery for the underhood so called back up battery and with those types the manual indicates a jump start.

spinn

are you still referring to a W211? I'm not aware there are different models within the W211 that utilize a different setup.

spinn

Anyone that replaced their Aux battery...did you have issues with the terminals not being threaded? Bought one from Batteries Plus and it wasn't threaded; came with some small size bolts and a square-ish nut that slips inside the terminal. Called around to Napa and Wal Mart, and their battery terminals are not threaded as well. What are people doing to make this work?

starbrite

I'd go with a Deka AGM @ $76 delivered, ETX14, 1 yr warranty : http://www.bohannonbattery.com/html/deka/etx14.html

Replaces GTX-14-BS that everyone's referencing

spinn

It turns out that the there was a threaded nut included that fit the factory battery terminal bolt. I got the battery from BatteriesPlus and they charged it up for me before I picked it up.

roboref

Just wanted to add my thanks for the help on this forum, post and other posts about battery replacement.

The knowledge shared was invaluable. I used a memory saver device and put main and aux. battery in for $215 plus the purchase of a 12 volt memory saver $12 at Autozone and a battery charge pack for the 12 volt supply for another $40. The independent shop I use is pretty reasonable but wanted $450 for these 2 batteries. So with this video and help. I did the job for $267.

Bought a Bosch Type 49 at Pepboys (AGM rated and 4 year free replacement) regular price $199, but had a 30% off if ordered on line and $20 rebate. So $120 total. Perfect fit.

Ended up using an Exide extreme duty XTX 14 BS exact fit but had to remove attached battery cable bolts and use the bolts that came with it. Sealed AGM type battery $75.

Also purchased a:

Schumacher (SCUINC12VOBD)
Memory Saver Adapter Cable

Converts a jumpstarter to an OBDII Based Memory Saver
Easy to read LED indicates connection
Extra long 78" cable length
Increase customer satisfaction
Provides speedier service
Easy to use adapter cable connecting from the 12V power port on a jumpstarter to the OBDII connector on the vehicle providing 12V power to back up on-board computer memory in devices and accessories during battery replacement.

Used it to maintain accessory settings while replacing main battery. Saved having to reset everything and is also supposed to avoid any issues of having the car without battery power.

Glad to have it done and thought I would just add my 2 cents worht.

Thanks for all the help!

wjcandee

Well, when you need a new battery, here are a few things to know...

The size of your main battery is Group 49, also known as H8, also known as L5.

If you want to do it yourself, THIS is probably the most reasonably-priced Group 49 L5 H8 AGM battery out there (and it looks to be an Exide Edge FP-AGML5/49): http://www.ruralking.com/battery-aut...-agml5-49.html

Or this one:
The AC/Delco is such a good deal at $145 that Amazon has trouble keeping them in stock. (Like they were out yesterday, got a shipment today, and are now back down to one left. Then it'll be a few days where the site either says "Usually ships in 1-2 Months" or "Out of Stock", and the process will repeat. Just keep checking, and it will turn up. Now it says Only Ten Left, even though they had a whole bunch earlier today.)

If you want to go with a non-AGM battery, as some people do successfully although there are good reasons to use an AGM Battery, this is a fine one, with the vent holes in the right place, etc.: http://www.walmart.com/ip/EverStart-...ttery/16782659

If you want someone to install it for you, I recently bought this AutoCraft Platinum AGM Battery, Group Size H8, which is the right one for the W211, at Advance Auto Parts. THEY WILL INSTALL IT FOR FREE, EVEN IN AN ML350 where it is located under the passenger seat and is at least a half-hour job. At our store, at least, the people really know what they are doing, and they do a lot of MB replacements. It's a fine battery, and for that price installed, hard to beat: http://shop.advanceautoparts.com/p/a...agm/10210828-P Advance Auto Parts will also test your current battery for free using a fancy-schmancy Midtronics tester, which is the exact brand that MB says you have to use to get an accurate result, and for the use of which they charge you at the dealer; the old methods won't give you the right answer with an AGM battery.

There is also Sears Die-Hard Advanced Gold AGM, where they will charge $30 to install it, and the Bosch Platinum H8/Group 49 AGM at Pep Boys. [Some Pep Boys will install it for free, and some will charge for it. You can tell by picking the store and your car on their web site, and seeing what it says, then booking it online if it says they'll do it for free. If it shows a charge, Pep Boys will always beat anyone else's quote by 5%, so if you show them in the store that Sears will install it for $30, they will always beat that. That's true for everything, tires, etc., so if you can get a written quote anywhere on the exact same service or product (i.e. a Bosch Battery, a BWD/Intermotor MAP Sensor, etc.) they'll match or beat that price.] Bosch and Pep Boys often have specials on that battery; right now, $169 when you include the mail-in rebate.

People on the forum who buy the dealer battery because it is "better" are on a fool's errand. And there is no advantage to having the dealer install it as opposed to yourself (if you're even a little handy). If you're not comfortable doing it (the thing is heavy), then just get any of the companies mentioned above to do it. There is nothing that the dealer does with regard to the battery that they won't do, and indeed companies like Pep Boys will use a memory saver when installing your battery so there won't be any need to reset anything after the old battery is disconnected.

AS TO THE AUX BATTERY:

If you're going to install it yourself (easy, really easy), the right size is 14BS. Get this AGM one from Amazon. (Don't get it from a marketplace vendor because your chances of getting a fresh, authentic one are maximized when buying from Amazon itself.). A lot of members here have installed it and YUASA is top-of-the-line when it comes to quality:


The instructions on how to install it in the W211 are about six down in the reviews section on Amazon when ordered by helpfulness. I used the instructions there and it was a cinch. There are also Youtube videos.

WalMart has an excellent AGM battery in the right size, for about $75: http://www.walmart.com/ip/EverStart-...ttery/16795217

Advance will also install their AUX battery for free: http://shop.advanceautoparts.com/p/a...4bs&showTitle=

The Advance one is NOT an AGM battery, but their customer service swears by it and says they install it in a lot of W211s. Similarly, Pep Boys has a ProStart 14BS non-AGM battery that they will install for free.

So...if you want to install both batteries yourself, you can have both at your door for $210 total.

If you want someone to install them, you can go the Advance Auto Parts route for $260 installed.

All these batteries will work fine. Folks make wayyyyyy too big a deal about them.

wjcandee

The nut that comes with the YUASA fits perfectly inside the battery terminal, and the bolt that is attached to the leads on the car goes perfectly into it. Hold nut with index finger under top of battery terminal. Stick tip of bolt through top of terminal and into hole in nut. Turn (righty-tighty) bolt head. SUCCESS!

wjcandee

I am mystified by what appears to be the logic of so many of our members:

"I'm getting those pesky lights, so I guess the battery is low." [correct!].

"So I guess I need to replace it." [Not necessarily.]

The reality is that if you are doing a fair bit of local driving, you're not fully-recharging your battery on a regular basis. The battery in our W211s doesn't need to be at 100-percent charge to function well, and routinely is running a good bit below that. As it gets a little older, and you're making a bunch of local drives in cold weather, it makes sense that you'll be getting those lights.

Why not try RECHARGING rather than replacing. Your car really isn't putting out a lot of current on that battery as you drive around, so it stands to reason that in certain seasons and in certain patterns of driving, after a while you're going to be draining the battery a good bit. [And remember that on the AUX battery, the car only charges it for a couple of minutes per turn of the ignition key, then stops applying a charge until the next time you turn the key.] That you get a light doesn't mean the battery needs to be replaced.

I'm not afraid to charge my main battery in the car, because I'm using an automatic battery charger set to run at no more than 6 amps, and it can't spark, and I do it with the trunk open (after the car has gone to sleep and shut off the trunk light) so there's plenty of ventilation, and I take all the precautions. I would recommend that you take the battery out to charge it, but I just do it in place. Schumacher 2/6/10 Automatic Charger, clamped to the positive and negative terminals on the battery with the wires still connected. NO, it doesn't fry anything if done properly (but you probably should have the car "asleep" while charging). Set it to the tortoise, runs for a few hours. And the main battery is nicely topped-off. If you think the AUX battery is the culprit, pull it out (it's so easy to do) and throw it on the charger at 2 amps until it is recharged.

Quick way to put off having to buy a new battery. And if you do this from time to time, you will extend the life of your batteries.

starbrite

@wjcandee...nice comprehensive post # 35, w/lots of good info.

Your post above, no need to pull the aux battery, if you're charging the main with the cables connected. The aux will charge as well.

wjcandee

Awww...thanks!!!

I'm interested in your theory about the AUX battery. The Mercedes piece on how the system works indicates that the BCU only energizes the relay controlling the circuit to that battery when the engine is actually running and only connects the battery into the circuit when it needs emergency power after cutting out two stages of consumers. It also only sends a charging current to the AUX battery for a few minutes per turn of the key. It's why, when mine was dying, I got the light to go off after taking multiple short trips around town, but if I took an hour-long trip to the City, the light wouldn't go out during or after that trip.

Given that, I am unclear why or how charging the main battery (G1), or putting a current on the circuit at the main battery, would send a charge to the AUX battery. Maybe it does, but I, at least, don't see how the structure of the system would cause it to do so.

Anyway, thanks for your kind words and your insights!!

Stuttgarten

I just read in Consumer Reports (CR) March 2015 edition, that Autozone's Duralast Platinum AGM Group 48 @ $165, should be avoided due to poor performance. Article on Page 58, expressed surprise as other Duralast batteries had earned CR Best Buy in their ratings.

They also added that Duralast AGM group 65 batteries had 4 units fail before 12 weeks.

wjcandee

Right, and we use Group 49. Consumer Reports's theory is that different battery sizes by the same retailer vary widely in performance. Not to be glib, but 48 and 49 are two different sizes.

Consumer Reports would have you believe as well that when Johnson Controls makes a battery labelled for one retailer, and a virtually-identical battery for another retailer, they will vary tremendously in performance. Maybe...

Also, none of their incredibly-harsh tests tell you much about how well the thing is going to work in normal service over 3-5 years. I didn't mention Autozone, but I'm pretty sure their AGM will do in a pinch and, properly-maintained (i.e. kept charged) in normal service, will last beyond the warranty. And if it doesn't, you can get a new one for free.

And just so folks who didn't read the article know, when they say "fail before 12 weeks", they mean "fail before 12 weeks of testing designed to replicate years of service in a short time", not "fail before 12 weeks of normal use in a car". The validity of their methodology is yet to be proven...

And in any event, I can buy five sets of batteries for my E500 for the price of one $1100 trip to the dealer, so I come out ahead regardless of whether the battery only lasts 3 years.

starbrite

I've always agreed with everything you state. I certainly have no rational explanation other than the two times my main and aux batteries were below 12 volts. Using a Ctek trickle charger (with the main battery's pos and neg cable connected) both the main and aux batteries came back up to full voltage.

ptkacik

The aux battery doesn't support the car. It is made to stay charged and only help the EBC brake control in case of an electrical failure. The idea is that if your alternator goes out or your battery goes dead, you can still stop the car.

This is why some electronic issues result in the "brake failure, take car to shop immediately " message. If the battery fails, then you've lost your brake backup system.

starbrite

Not entirely true ptkacik. See attached.

ptkacik

Starbrite: I see what they say but don't think it changes much. Did I miss something or is your view that the aux battery is used to back up other things besides the brakes? I would guess that you are right about that but I heard that they put it in because of the brake requirements.

My point was to explain why it is there at all and not be a definitive electrical description.

BTW, despite all the bad mojo about the EBC, I love my brakes and the additional features they provide. I especially like the quick highway response.

wjcandee

I love my brakes too. It's like anti-vaccine hysteria what killed it.

I think the confusion about your statement was your use of the word "only". As in it's "only" there for the SBC brakes. It isn't. It's there as general support for the electical system, but the impetus for it was most likely, as you say, to assuage fears about loss of brakes. Note that plenty of MBs these days, like the ML350, don't have SBC brakes but nevertheless have a second (albeit smaller now) battery.

starbrite

Exactly, couldn't have said it better myself. The general misconception is that it's only purpose is for the SBC. Ironically, the MB tech page (from technical training material) I posted, doesn't mention SBC at all.

cybertronicify

You do not ever want a big LiPo battery inside a trunk of a car. Those things are deadly and unpredictable, any small error and it will swell up and explode/catch fire. You are better off going with a much more stable type of lithium battery called LiFePO4. Those things you can abuse the hell outta them and it won't do much. Get an axe and split it in half, all it will do is give off a bit of smoke. Li-ion is good too but is usually very heavy and can't deliver much amps.