It also controls a HOLD function.

 

THanks Randall, I'll look into the control unit angle.
Happy Easter and thanks for the quick reply.
Allan

 

Never used it. Hold on a hill? Seems unnecessary without a clutch.

 

Good luck and Happy Easter. Stay safe and well.

 

​​​​​​It seems to me that I mean the hold function, for holding the car in drive mode without pressing the brake, when for example you expect a green traffic light. It is activated by short pressing the brake. It's comfortable.

 

Exactly and it is very useful (all MBs have this feature for years now). Seems OP is not aware of it.

 

I find it very hard to believe that a battery that small is expected to reliably restart the car's engine...possibly over and over again over a short period, depending on traffic conditions. The spec on that battery suggests it might work OK in a medium-sized motorcycle. Doesn't seem very MB to me. I'd have to read it in a factory service manual before I'd believe it. This "Hold" function sounds more credible, but I don't know why they wouldn't use the main battery for that. Or, it might power the top motor...if it has the same spec regardless of whether a 450, 550, or 63, then that's a far more likely application than as a starter battery, though I guess it could be there to just help pick up whatever load might be on the electrical system while the engine/alternator stops.

 

OK, I dove into the "installing a charging pigtail on the auxiliary battery" project. Taking my time due to all the fear that was instilled in me after reading the rest of this thread, it took me about 1/2 an hour to expose the aux. battery (the same FIAMM unit mentioned by the OP) using only hand tools. I could easily do it now in less than half that time. Once I had access, I discovered that the pigtail that came with my CTek charger was actually a bit short...ideally, it would be three or four inches longer to allow routing out of the enclosure neatly. While I was pondering that drawback, I decided to check the voltage on this, the original battery (week 39 of 2016). It showed 12.85V with the leads still connected, and after an afternoon of messing around with the electronics while learning the car. This has me thinking that, even though the battery is almost four years old, it seems to be doing fine without ever having had any special attention regarding charging...and the car had sat on the dealer's lot for over three months. Then I bought it, drove it home (3 1/2 hours), and parked it with a CTek on the main battery for a month before measuring the aux. battery's voltage. Right now, my aux. battery seems to be doing just fine so, absent a longer pigtail for my charger, I decided to button everything back up without adding charging capability, for the time being. A couple of things, though: this battery has a very specifically-located vent hose, so whatever you replace it with will need to have a similarly-located vent nipple for its hose as well. The other thing...the screws holding the power leads on the battery's terminals were just barely more than finger tight. I don't understand why the car's motion/vibration over its first 21,000 miles hadn't resulted in one or both cables coming loose, but neither did, and the battery did have a good charge on it so...

 

Nice write up Dr. Manhattan. Can you describe in more detail how you obtained access to this battery? I am pleased to learn that your auxiliary battery has retained its charge. I was going to do the same thing and install a pigtail in my battery so I could use my CTEK to keep it charged as well but after talking to the Service Manager at my local dealer he convinced me that it was unnecessary. I still am interested in being able to maintain this secondary battery with a CTEK as my SL is not driven daily and does sit for several weeks without being driven especially in the winter months. Thanks.

 

My SL was stored in my unheated garage this winter in Western NY for about 4 or 5 months, with the trickle charger on the main battery only. In April when I went to fire her up she started just fine and everything worked fine.

FWIW.

 

This is good news. I guess my dealer was correct when they said the auxiliary batteries hold a charge very well. Perhaps when they certified my car they replaced mine. One of these days I'll try to access it and see if I can find a date code. Too damn hot now, I'll wait until cooler weather.

 

Did you use gas Stabilizer?

 

Yes I did. I was also surprised that there were no flat spots in the tires after sitting for that long. Maybe the runflats are less susceptible to that. Other convertibles I've stored the same way were a little bumpy on the first spring drive for the first 10 or so miles.

 

I started with page 285 in my '17 owner's manual, where it tells you how to remove those two trim panels that cover the battery/fuse box. It goes just like it describes. First, send the passenger seat fully forward with the button on top of the seat, above the belt release, Then, slip your fingers under the bottom edge of the front panel and pull forward. The bottom of the panel may come loose first, or the whole panel may come off with one pull. If it comes bottom first, then slide your fingers up the sides of the panel and keep pulling. There are two long horizontal tabs on the top rear of the front panel that engage holes in the front of the battery cage, but they point straight back so if you're pulling forward you won't have any problem with them. Once that panel is free, grasp the front edge of the top panel and pull up. The top panel also has two hooked tabs on its rear edge that engage holes near the rear of the top of the battery cage, so the panel will initially come up as though it's hinged at the rear. You'll quickly see that it can just be pulled forward a bit to disengage these tabs, and then the top trim panel is also out of the way.

Now you're looking at the scene in the first photo that D49 posted above. Without going any further, it looks like all you have to do is remove all eight T30 Torx screws and the cage will come right off...but, no. Go ahead and remove all eight screws, but then you will find that the top trim piece on the back of the center console (the one surrounding the "accordion") is also in the way, because the battery cage has two sizable nubs on its inner end (the end by the center console) that are captured underneath the side edge of the top rear center console trim panel. No worries, the top trim panel comes off easily by pulling upward along the sides of the panel, starting near the front. There are, I believe, three tabs (front, middle, rear) along each side of the top trim panel that will pull out of their clips as you apply upward pressure. This panel will come off like the top trim panel on the battery cage did...that is, it will tend to hinge upward, front first, as the back of the panel extends quite a way into/under the rear bulkhead trim panel that surrounds the back of it. Once the three tabs on each side of the top panel are disengaged, just pull forward on the panel to free it from the rear bulkhead panel.

Now, for the only semi-P.I.T.A., and even that's doable with a bit of care. The battery cage has to come forward a bit in order for it to disengage from the rear bulkhead trim panel, but there is interference on its outboard rear corner and the forward nub on its inner end. So, looking at the first photo above again, you see the narrow red leather trim strip coming in from the right side of the picture...the long narrow strip that is right underneath the now-removed "accordion" trim panel. There's red light coming out from under it. That trim strip can be popped loose by working it straight out horizontally away from the center console, but the inner rear end of it is hooked on a vertical guide, so it will have to be lifted vertically just slightly to disengage the guide. Before doing so, there are horizontal retaining pins every three or four inches along the length of this strip, a few of which will need to be released so you'll be able to lift the rear end of the strip off of its guide. Once the strip is free of that guide and the the console, you can lift and twist the end of it just enough, while finagling the battery cage, to get it up over the corner of the cage and out in front of the cage. Now you're finally home free. A little more finessing of the cage and the strip, and the cage is out of there. The battery still has a soft plastic cover over it. That cover is hinged along the inner edge, and there are two clips on the outer edge that are easily released by pressing them outward (away from the console) with your fingers. Once they're released, open the cover and it will likely just come off in your hand, as the hinge is designed to disengage from itself. There's your battery...and a lot of fuses!

By the way, I know I read somewhere that someone had removed the rear bulkhead trim panel (the one that runs across the car behind the seats) while doing this project. I have no idea how easy that is to do, but if it's not too bad it might be a better way to go than going through my last step with the console trim strip. It would remove the worry of possibly breaking something while finessing the strip. With the bulkhead panel out of the way, the battery cage would probably come right out, without messing with the trim strip like I did. My explanation of how I dealt with the strip even has me scared, and I've already done it with no problem. It was much easier than it sounds.

I have a decent imagination, but the only explanation I can come up with for MB to have placed an almost-permanent closed cover over this stuff is for the sole purpose of preventing us from checking/replacing our own fuses and/or battery. I'm more pissed about the fuses, myself. If you look at D49's second photo, there is a large green fuse (30A) right near the top of the pic. I don't know what that one is for, but mine had worked its way almost all the way out of its socket, so I set about pushing all the fuses inside there back down into their sockets..and there were only a couple that didn't move. Some fuses are prevented from coming all the way out by plastic retaining bails, but several are not. My car is buttoned back up now, but if I find a longer pigtail for my CTek and head back in there, I'll be opening an access window in the top of the cage so I can at least check my fuses without having to tear apart half of my interior each time.

I hope all this helps someone...

 

Some serious dedication for Dr. M to type that all out. Employee of the month!

 

I second that, awesome post. When the weather cools down I plan to access this battery and install a pigtail so I can try to extend the life of the battery. Thanks very much!!

 

Jeez...after I finished that and hit send, I though "man, that's probably way more information that anyone wanted". I'm sorry if it is, but I didn't want anyone who might be so inclined to hesitate needlessly. If I do go in there again, I'll be taking a closer look at the possibility of removing the bulkhead trim panel instead of messing around with the console trim strip. I should also add that I've driven the car for a couple of hours since re-assembling everything and there are no squeaks, rattles, etc. It all went back together the same way it all went in initially on the assembly line.

 

Post was great and much appreciated.

 

I agree that there is only one reason why MB makes removal of the auxiliary battery so difficult. I too was pissed of, so my solution was to remove the screws holding the battery cage. Then pulling the thin trim strip which runs along the bottom of the console back. I then took a hacksaw blade and cut off the two pieces of plastic which were preventing the removal of the battery cage! Worked perfectly. Took five minutes to cut the two plastic extensions which prevented removal of the cage. Once removed the cage was removed easily without having to go through removal of additional trim pieces. In the future, removal of the cage will simply require removal of the hold down screws, and pulling back the one trim strip. I first made sure I wouldn’t be contacting any electrical parts by using a wooden chop stick to make sure I wouldn’t be cutting through any serious parts. The chop stick let me see there wasn’t anything serious underneath that I’d be contacting with the end of a hacksaw blade (not attached to the hacksaw). I proceeded slowly making sure I didn’t extend the blade too far past the plastic extensions. No problem, those extensions are gone forever. I was careful to make straight cuts which I filed smooth once the cage was removed. I used a small wood wedge between the edge of the cage and the console after placing some blue tape on the area of the console where I placed the wedge as well as along the areas where I would be using the saw blade. In looking at the cage in place now, only a MB mechanic would know I defeated their attempt to screw an owner up. The edge is straight and true and nobody would even notice what I had done.

 

Just replace the main battery on my 2013 SL550. It was the original unit on my DD with +99,000 miles. Never had a problem but during Schedule A service the dealer advised its change. Not a huge surprised because a independent tech warned the battery was loosing power over a year ago. After 7 years of service, I couldn't complain. Had just seen my wife's Caddy's battery die with no warning so I didn't want to take any chances. I'm told that behavior is typical for batteries in the Phoenix area. The only problem was the dealer didn't have any. Moreover, he said it has been a particularly bad summer for batteries and he had about 5 other car waiting and the battery was on back order. I didn't want to wait.

After a search, I found a compatible DieHard at an Advanced Auto Parts for about $220. Wanted them to put it in but they didn't have a way to maintain computer codes. I had heard the same story from other auto supply stores. The result it turned into a DYI. Very easy once I found a neighbor who had a way to keep the system charged. Hardest part was locating the jump posts under the hood. (Passenger side near the firewall. Look for red cap.) Battery change is very easy with the right sockets, 10mm & 13mm.

Point of the story is that I will not hesitate to do it myself again.

 

Excellent work. Thanks for taking the time. All of this I do know, however, many do not.

​​​​​​​Joseph

 

What a carry on just to get at the fuses. I also have been scratching my head trying to work out how to remove said cage
Thanks for the info.
BL

 

I didn't think there were any issues when changing the main battery, as the Aux would take up any slack eg radio / command etc.

 

What did you use as a voltage source "to keep the system charged"?

 

I'm curious, how much was the battery and how much was labor?