Which Mercedes R230 SL model to buy, and how to avoid a fire with CATASTROPHIC damage.....

[@frankmattingly356]

Mike, your videos are AMAZING... so detailed, thorough and well choreographed. Every single R230 owner should watch these masterpieces. Thank you so much, without you I probably would have sold my car. Bless you Sir!!!

[@MikesMercsandothercars]

Well that is very kind of you to say so. My wife describes my videos as the most boring thing she has ever been subjected to.....but there again she doesn't get involved in fixing cars..... Mike

[@frankmattingly356]

@@MikesMercsandothercars Mike, I don't want to invest the money to chase down the parasitic leak in my SL600... I just don't drive the car enough to worry about it. I put the charger on it every couple of days, but I know this severely degrades the battery over the period of about a year. If I put a battery disconnect on the back battery and just turned it off when I "park" the car for a couple of weeks, is that a good idea? Would that hurt anything. Just trying to figure out a simple solution. Thanks again for all your help.

[@MikesMercsandothercars]

@@frankmattingly356 Hi - Christmas is almost upon us and you could put a Fluke 325 Clamp meter on your list to see what kind of draw your car has. Failing that, you can get thermal imaging attachments for smartphones that might help you quickly determine where the problem lies... Disconnecting the consumer battery when not in use, doesn't harm anything. You might lose a few saved settings but I do this when I go away to Australia. Mike

[@frankmattingly356]

@@MikesMercsandothercars Thanks Mike, all great suggestions. I will probably just do the "switch"... simple. Thanks again for all you do for the R230 owners out there.

[@sayedaskari1]

Can you kindly link to the trim removal in the trunk? I havent been able to find in your channel. Thanks for a lot of beneficial content-

[@MikesMercsandothercars]

My pleasure - here is the video detailing how to remove the boot trim to get to the BCM: kzbin.info/www/bejne/i3anhZubZZV1eck It looks scary....but if I can do it anyone can. Mike

[@Brian_L_5168]

Hi Mike, your understanding of Mercedes & electrical knowledge is out of this world ! ! Is there any telltale signs when BCM is on its way out? Meaning if you connect Star Diagnosis, Autel, or high end scanner, what trouble codes should we be looking for?

[@MikesMercsandothercars]

Hi - one early warning signs of a failing BCM may be a red battery warning light on the dash....and possibly a flat starter battery under the bonnet. As far as I am aware, the car wont throw any warning codes before the red battery warning icon appears on the dash. Ideally, I would advise every owner to take the trouble to remove their BCM, open it up and have a look inside to make sure there are no early signs of charring. It is much easier to get these repaired BEFORE the board starts melting. My video on fixing the rear ABC sensor shows how to get to the BCM: kzbin.info/www/bejne/i3anhZubZZV1eck My 2nd piece of advice is to avoid frequently letting the consumer battery run below 11.8v as this draws a lot of current through the BCM to recharge it. Leaving the battery is a state of discharge for any period of time will quickly ruin it. Personally I prefer to remove the battery to recharge it if my car has sat BUT....many people report using the CTEK trickle charger without problem. Mike

[@ftffighter]

@@MikesMercsandothercars I bet if you timed the discharge rates and time how fast your BCM works, you might be able to find a safety parameter at least.

[@MikesMercsandothercars]

@@ftffighter Yes - one of the things I plan to do is drive with a thermal imaging camera pointed at the BCM under various condition...eg consumer battery completely flat, 50% discharged and full charged to see if there are significant temp differences...then maybe repeat with a flat starter battery etc. Mike

[@rayblackard1974]

Have an 04 late production 500sl with the AMG badging, wheels, & trim 600 engine. Was my dream car & of course i couldn't afford new. Got from estate sale 8 yrs ago. Just turned 63k miles. Beautiful awesome performing car. Unfortunately havine to sell due to spinal deterioration. Hard as hell to get out of now. Has been a great car, replaced ABC 4 yrs ago ($$$$). Will truly miss the joy driving it.

[@MikesMercsandothercars]

yes - I just drove my SL55 to London and back and what an exhilarating drive it was! One of the functions of the ABC was to make it easier getting in and out of the car.... another was to be able to raise the car manually to enable snow chains to be used. If I ever sell mine, I'm sure I will miss it too!. Mike

[@Michael.Chapman]

I guess my 2005 E350 with SBC and dual batteries is subject to the same problems? Thank you for the advice! I was getting daily warnings re convenience functions on start-up-until the accessory battery was replaced. It still gives the same warning if I don’t drive for a week or so.

[@MikesMercsandothercars]

Not sure about the E350, but on the SL55, a fully charged consumer battery will last about 2 weeks with a constant draw of less than 50mA. Mike

[@Michael.Chapman]

@@MikesMercsandothercars Thanks Mike🙂👍, ... Mike😀!

[@MikesMercsandothercars]

@@Michael.Chapman No probs. there are 5 other 'battery related issues' in the playlist below - these might help you diagnose any potential problem: kzbin.info/aero/PLONqXqFnLGrjrRMyMj-02uPxLVogBjr8a Mike

[@WindsorGoldPlating]

This guy is a genius! Thank you

[@MikesMercsandothercars]

Well..I don't know about that, but thanks for the kind comment. Mike

[@fieldgunbio2402]

Oh that was a good lesson to learn, never thought to take the battery off to charge as recently during storage, the consumer battery dropped off so i put the trickle back on then someone suggested using there charger to fire in the charge :( oh dear, hopefully I've not fried the unit, in the few hours it was hooked up. Live and learn.

[@MikesMercsandothercars]

Well if it’s any consolation, you would not be the first to inadvertently mistreat the consumer battery and accompanying battery control module. Mike

[@cav4290]

Hallo Mike! Great to see you showing this - will hopefully save many R230. You should post a video showing how to add a fuse to the BCM.

[@MikesMercsandothercars]

Yes...your original video actually inspired me to research this topic more thoroughly. Thank you. One day when I have the time, I will hook up a thermal imaging camera and actually monitor what is happening at a component level in the BCM. Call me a crazy but...I'm not going to add an additional fuse on my BCM because I don't think my car is very original and thus in my opinion (famous last words?) is not a candidate for a fire. Mike

[@cav4290]

@@MikesMercsandothercars Adding a fuse is easy and there no "structural" or permanent changes. I strongly recommend you do it, as in fact your car is an ideal candidate due to the lack of use. There is a company in Germany that specializes in rebuilding these units, last I heard they have a lot of work - so that should tell you something.

[@ssyy6969]

Very nice explanation 🎉

[@MikesMercsandothercars]

Thanks - have you got one of these cars? Mike

[@ssyy6969]

@@MikesMercsandothercars I have a like new SL 04 amg package

[@MikesMercsandothercars]

​@@ssyy6969 Nice. A friend of mine bought this SL55 new for just under £100k and I bought it from him with less than 40k miles on the clock. It is an exhilarating car and some of the other video in the playlist below may be of interest to you: kzbin.info/aero/PLONqXqFnLGrjrRMyMj-02uPxLVogBjr8a Mike

[@ssyy6969]

@@MikesMercsandothercars I have Seen a lot of your videos excellent information as my SL only Has 20k miles

[@dpbroughton9319]

Thanks very informative for perspective purchase of this marque.

[@MikesMercsandothercars]

You are welcome. I have just purchased a re-engineered version of the BCM and will hopefully be doing a video on this subject soon. Mike

[@ag-fd1py]

Great info thanks so much Mike. Don't use my 350 much and seem to need a new consumer battery every 2-3 weeks. Does it draw more current locked or unlocked? Have seen a battery disconnect device for sale on amazon using a fob after locking the car, any thoughts? Wonder how much longer an agm battery would last compared to a cheapy? Anyway, very grateful that people like Mike and other experts in their fields post here.

[@MikesMercsandothercars]

Probably the best investment you can make if you own an R230 is a decent clamp meter like the Fluke. This will tell you if you if your car is drawing more than 56mA when asleep. If you look at some of the other videos in my SL55 playlist, you will see that my car had 3 separate issues when I got it. Having sorted those out, a decent AGM battery will last 2 weeks without ‘consumer battery warning’. This is with the car locked. The battery itself should last several years. Mike

[@ash44roberts44]

Hello Mike, thanks for posting this very interesting video… I was somewhat alarmed to hear your warning regarding trickle-charging. I’ve been using this method on my 2005 SL55 for 12 years now. It lives in Spain so there are long periods when I don’t get to use it. I use a CTEC MXS 5.0 on the consumer battery in the boot and have experienced no problems to date. The batteries were replaced by an authorised Mercedes workshop a few years ago and I’ve owned the car from new. It’s covered 78,000 miles but still looks like a relatively new car. What are your thoughts? Thanks, Ashley 👍

[@MikesMercsandothercars]

Hi - I reckon you should be just fine with the CTEC. the problem lies with some of the cheaper trickle chargers which can have a voltage spike when you connect them. That wouldn't usually matter if it was just charging the battery, but in the case of the R230, the trickle charger is also connecting to the BCM. Its a bit of a pain, but if my SL55 has been sitting for so long that the consumer battery has run below 11.8v, I take it out and recharge it....this saves putting undue stress on the alternator/BCM which are not really designed to charge flat batteries. My car was owned from new by a friend of mine....they weren't cheap to buy!! Mike

[@ash44roberts44]

@@MikesMercsandothercars Thanks Mike, I’m looking forward to getting my SL55 out again at the end of the week when we go back to Spain. As you say they were certainly not cheap to buy 20 years ago; I needed a second mortgage! 🤣

[@MikesMercsandothercars]

@@ash44roberts44 Back to Spain next week? I'm not jealous at all....

[@MegaRugby2]

Buy a small dedicated jump start battery.

[@MikesMercsandothercars]

@@MegaRugby2 NO. Best advice is to never jump start these cars. The front starter battery rarely goes flats as it is only ever used to start the car. If your car isn't starting, you either have a faulty starter battery or more likely......a problem with the battery control module. Mike

[@harnas3848]

Just double checking as unfortunately some people are of a different opinion on the order of connecting / disconnecting the two batteries. Do we always connect / disconnect the battery in the back whilst the front battery is connected?

[@MikesMercsandothercars]

Yes. ALWAYS disconnect rear battery first, then starter when removing both batteries. Conversely, you should connect starter battery first and then consumer when reinstalling. Mike

[@harnas3848]

@ thanks for confirming. The issue is even on Facebook BCM group there are some members who say the opposite and they you get yourself confused....

[@MikesMercsandothercars]

@@harnas3848 Yep...that can be a real problem with the internet. People read stuff and take it as fact. I'm just in the process of doing a video about the R107 soft top and almost every video I have seen is doing it wrong! Mike

[@FiftyTechSolutions]

Thank you very much for this really informative video!

[@MikesMercsandothercars]

You are welcome - thanks for watching. Mike

[@Nilfaultfound22]

Brilliant video Mike, sooooo complex. I'll stick with my 560 :)

[@MikesMercsandothercars]

Thanks for your comment ……yep the R230 sure is complicated vs the R107. Mike

[@lightdiodes]

Great movie Mike, I have just bought an auction SL55. It seems well maintained however it was in transit for couple of months, the rear battery went completely dead, cannot tell if it was jump started by the logistics folks or anything. I'm thinking about taking it to the dealership for general diagnosis, do they understand the issue and have proper procedures to inspect BCMs and their condition? What is the general recommendation for a long-term storage? I was thinking about disconnecting both batteries according to the procedure in Owner's manual however I read reconnecting them back may lead to another current peaks that may have an impact on the BCM condition. What are your thoughts?

[@MikesMercsandothercars]

Congrats on your SL55 - was it a UK auction? Here are my thoughts: No need to ever disconnect the front starter battery as these rarely have a problem and will maintain enough charge to start the car for months. Many people use a CTEK trickle charge to maintain the rear battery which is one option. Personally, I prefer disconnecting the rear battery and charging it out of the car if I’m not using the car. My garage is remote without power which is one influencing factor. Personally, I wouldn’t spend the money taking this car to a dealer for a general diagnosis. The two best investments you can make are: 1. Fluke clamp meter to diagnose battery drains 2. High end scanner to diagnose and clear faults These cars really benefit from being driven to ensure that the ABC hydraulic fluid is circulated. I believe you will increase the longevity of your ABC suspension by regularly changing the hydraulic fluid. That is one thing I would definitely spend money on. My advice would be to take a look at the BCM yourself….it might seem scary taking your car apart, but if I can do it, anyone can. Just have a look at the SL55 playlist on my channel for guidance. Mike

[@lightdiodes]

@@MikesMercsandothercars The car is from Japan and I have disconnected both batteries according to the procedure from SL's user manual. I'm looking to inspect the BCM myself today/tomorrow. Do you think adding a smaller gauge cables together with a 30A fuse before the BCM solves the issue? I saw this video over here by another UK SL lover and I wonder if this prevents all the issues or just some of them. kzbin.info/www/bejne/oZCnY5t5ebJ4eLM

[@MikesMercsandothercars]

@@lightdiodes I don't think connecting a fuse does any harm....whether it actually prevents damage to the BCM is of course another question. If your BCM is damaged or shows signs of charring, there are a couple of companies which rebuilt them with more modern components for about £500. Mike

[@lightdiodes]

@@MikesMercsandothercars Thanks, I have already found a company in my area which does the rebuild. Final question from me I guess, so I can explain this case to my car electrician: what is the root cause or design flaw of the factory BCMs that causes all the issues?

[@MikesMercsandothercars]

@@lightdiodes The million dollar question... Those BCM's were made with old style electrolyte capacitors which degrade over time and can leak electrolyte onto the board. Modern versions tend to be made from ceramic. Some surface mounted capacitors SMD's are made from a material which is prone to absorbing moisture from the air and this can cause premature failure...as can surge currents. Shorted capacitors in the voltage regulators could also be the issue. In a failing BCM, in most cases, you will see signs of burnt/blown Blue 470uf capacitors, blown MOSFET's, and burnt/blown SMD capacitors. What is the company you have found that can repair these units? Mike

[@jayjohnson8807]

Hi, watched your video explaining the BCM failure. I’ve had my 2005 SL500 for nearly 4yrs and I replaced the starter battery approximately 6-8 months ago and I did do the battery replacement procedure and I’ve noticed that I would randomly get the RED battery warning for about a week or two apart but, it goes away. I’ve never jumped started another car at all so I connected my scanner to it and it says something about the K57 relay and BCM. What is causing this and what do I do to fix this problem?

[@MikesMercsandothercars]

Hi - if you are lucky, you may just have a faulty K57 relay BUT if it was me, I would definitely go to the trouble of having a closer look at the BCM and check for signs of charring. Usually (not always) cars give out little warning signals for those who care to listen...a strange noise... a random warning light etc. The video below gives a detailed guide of how to get to the BCM.....this was the first job I had to do on my SL55 - it looks scary but if I can do it, anyone can. Mike

[@simonjones4776]

Got me worried now. I leave my sl55 rear battery on a ctek charger all the time in my garage as it is only driven maybe once a month. Maybe I should fit battery isolators instead.

[@mozartcarclassics]

Same here

[@mattmay2173]

I have both the battery’s on cteck’s . Might alternate them after watching this

[@MikesMercsandothercars]

@@mattmay2173 Hi - unless your starter battery is knackered and no longer holds its charge, it should easily last a few months. A new consumer battery with no parasitic draw will generally last 2-3 weeks before you get the consumer error message. Part of the problem is that many people have let their consumer battery become sulphated over time and it no longer holds full charge- this means that every time they use the car, the BCM is engaging relay K57. In that scenario, it is probably better to fit an isolater and put up with the hassle of losing some memory settings. Mike

[@simonjones4776]

@@MikesMercsandothercars Wonder if I could just isolate the bcm while parked up

[@mattmay2173]

Yer i think i will fit some isolator switches. Seems easy enough.

[@simonjones4776]

Would be handy to fit an access panel for the bcm in the boot. I would like to do that but not sure of the exact dimensions to cut an access.

[@MikesMercsandothercars]

Yes - I have thought of an access panel and I know some people have done this….and even wired in an additional fuse. Personally, I like to keep things OEM and avoid cutting holes. Maybe I’ll get hold of a spare piece of boot trim from the R230 graveyard and work out the dimensions. Mike

[@simonjones4776]

@@MikesMercsandothercars Today I cut a neat U shaped access using a sharp stanley knife. It was fairly easy and the carpet fits back in perfectly. Looks fine.

[@MikesMercsandothercars]

@@simonjones4776 ....maybe you have missed your vocation in life and could have been a carpet fitter? Thanks for the update. Mike

[@CL500MBZ]

Mercedes should have created a modular trunk access panel to allow easy access to the various devices for easy access and repair.

[@MikesMercsandothercars]

@@CL500MBZ Yes - agreed. Having to take half the car to pieces to access important modules like the BCM...and things like the hydraulic cylinders is a right old pain! Mike

[@dominicwood3750]

Very informative one extra point do not close the boot with the aux battery disconnected! I always leave a towel over the lock as a reminder

[@MikesMercsandothercars]

With the battery disconnected the central locking wont work so I guess the boot wouldn't automatically lock unless you used the blade key in the fob? I must confess, I have never tried closing the boot with the battery disconnected. Mike

[@m60kaf]

I'd change this advice to test the emergency blade key before disconnecting the battery - it will close but not soft close

[@MikesMercsandothercars]

@@m60kaf Yes - good advice. I somehow locked the keys in my car once only to discover that the blade key didn't actually fit the lock! Mike

[@kevinx2381]

A very informative video. However having studied the the area of the control box, in my opinion the course of the failure/fire is water ingress. a lot of rusting of bolts etc. I do not think the rusting is from the fire extinguisher use, it would only be superficial rust and the area would have been covered by trim so may not have been exposed to the extinguisher. the rust looks well established to me. I look forward to your comments as you have seen it up close and personal!!!

[@MikesMercsandothercars]

Thanks for your comment - that car in CoPart is one of many I have seen. Some of the the BCM casings have been in pristine condition with no signs of water ingress. Whilst water ingress is definitely a problem in these cars, it mainly affects the PSI pump on the other side of the trunk and the SAM units. Mike

[@mikeclinch1141]

I agree if you get water in the BCM you have an unfused connection to the systems battery so there is no protection of short to ground.

[@BobBenz55]

Have a SL600 and SL55. Nice info bro 👍🏼👌

[@MikesMercsandothercars]

Thanks. Nice cars you have. Mike

[@BobBenz55]

@@MikesMercsandothercarsreplaced my rear battery on my SL600. Much better now 👍🏼…. My SL55 has a weak start up. That one next. 👍🏼

[@MikesMercsandothercars]

@@BobBenz55 It will be interesting to find out why your SL55 has a weak start...hopefully just a dud starter battery. Mike

[@BobBenz55]

@@MikesMercsandothercarsI ain’t that lucky with these cars mate 😂… my favourite cars are the W124’s love working on those 😇

[@juaniglesiasgarcia7269]

Great video!!! Thanks!!

[@MikesMercsandothercars]

Thanks - do you have a R230? Mike

[@juaniglesiasgarcia7269]

​yes ​, I have a 350 with the m272 and 7gtronic. And also a Cteck, but allways charge accesory battery outside the car 😊

[@Raven431]

I want the sl55 to replace my supra, but im scared to death of the running costs

[@MikesMercsandothercars]

Well - a healthy dose of realism is a good place to start. The single biggest problem with the SL55 is that it looks like a normal car….and not like a super car. When you see a McLaren with hydraulic suspension you instinctively know (and expect) it will be expensive to fix…..similarly you know that the folding roof on a Ferrari California is going to be expensive to repair….the problem is, that you can pick up an SL55 for 10-20k….and perhaps the last owner didn’t have the money or inclination to service the car properly…change the ABC fluid regularly etc etc. This car is exhilarating to drive and I’d be looking for low mileage 1 careful owner from new type of car with heaps of service history. At 70,000-80,000 miles certain ‘expensive’ things will start needing to be replaced. I can’t really afford one of these cars but it was always my dream car when they first came out. My plan is to try and do everything myself starting with zero knowledge…..and in the process hopefully demonstrate that it is possible to drive and run a super car on a budget. Mike

[@MegaRugby2]

For good reason need pre purchase inspection and a good independent mechanic

[@MikesMercsandothercars]

@@MegaRugby2 Agreed. The problem is, that the R230 was a very technologically advanced car when it came out (ABC, SBC, BCM etc etc), and experts on this model are far and few between. Mike

[@CV-wo3qm]

Such a helpful video

[@MikesMercsandothercars]

Thanks. Mike

[@SunilPatel-lu3pd]

Hi all, new to a 2004 SL55, previously only had Audi, BMW and old 996s. People say not to connect the ctek to the direct negative battery terminal. As the car only arrived yesterday, could anyone offer advice on where to ground it - the car is stored outdoors on a drive so I have to run a flat power cable into the boot, the 996 allowed via cigarette socket which I could slip through the side of the door glass but I understand the merc cig socket does not stay live. What would be the best way to run the cable into the boot please? Thankyou

[@MikesMercsandothercars]

Congrats on your SL55. I never use a battery charger when my battery is in situ BUT I reckon any nut or stud connected to the body of the car would act as an earth. If you want to check whether a nut is connected to earth, just set your voltmeter to resistance and hold it between the negative terminal of the battery and the nut...and there should be continuity eg no resistance. I imagine the best way way to run a cable would be on the horizontal section of the boot by the boot lock. As a matter of interest, a good consumer AGM battery should last about 2 weeks before giving an 'consumers offline' message...and the SL 55 will nearly always start no matter how long you leave it standing because of the front starter battery. Mike

[@SunilPatel-lu3pd]

Thankyou Mike, I’ll leave it for now then as the car was driven from Devon to South London on Wednesday and I don’t want to leave the charger on whilst I’m away for a week Thursday so hopefully it will be ok but I’ll give it a run tomorrow. Very useful video by the way 👌

[@MikesMercsandothercars]

@@SunilPatel-lu3pd 9 times out of 10, the consumer battery in these cars is knackered because owners have let the battery run below 11.8v and left it there for weeks at a time which kills a battery. If you get a chance, take the battery out, make sure it is an AGM battery, charge it with an AGM charger over night....and then watch to see if it maintains a voltage of at least 12.6 to 12.7v after a few hours of being out of the car. One thing I have found invaluable to track down consumer battery drains is the Fluke clamp meter detailed in the video below: kzbin.info/www/bejne/poKvaqJvjq-bbLc Mike

[@m60kaf]

Waaaaaaaaaaaaaaaay too long. I fail to see why mercedes servicing prevents them going on fire. Seems to be established thinking that the caps dry out.... but what is VERY interesting in this case is that isn't an AGM battery, infact it isn't even a good quality ordinary battery (So I get your point that if it had Mercedes serviceing it would have an AGM and may not have gone on fire, but any decent garage should put the right part in)... Also intelligent trickle chagrders are not an issue and you are right about what you say about jump starting from front and if you trickle charge do it from the boot

[@MikesMercsandothercars]

"Caps drying out/degrading" may indeed be a contributory factor in these fires BUT the question to ask, is why do caps in some R230's degrade faster than in others? The main reasons for capacitors degrading and reduced lifetime is: "excessive application of operating voltage, reverse voltage, or ripple current"... When the BCM's were originally designed, it would have been difficult to test what happens to the 20-40yr life span of a capacitor under abnormal conditions like - incorrect battery, constant flat battery, jump starting voltage spikes etc. I guess if I bought an R230 with unknown history, I would be tempted to take out the BCM and have the capacitors replaced as a precaution. Other hacks like adding an inline fuse don't really address the root cause. Mike

[@gotglasses]

Keep car on a good ctec trickle charger on the consumer battery in the garage and you won’t have these problems .

[@MikesMercsandothercars]

Yes a CTEK trickle charger is what Mercedes recommend but......some people (like me) dont have power in their garage so that is not an option. The other thing to note is that not all trickle chargers are born equal. Some of the cheaper models can generate a voltage spike when you first connect them. Mike

[@raymonheath1436]

Simple answer, buy an r172 slk 350 with all the options for the same price, faster, more reliable , does not leak cheaper to fix, I absolutely love mine , it is perfect for to long haul, the twistys being bothe

[@MikesMercsandothercars]

Thanks for your comment which has got me thinking....I reckon it would be an interesting video to do a comparison between a modern R172 350SLK vs and a 2004 SL55 AMG. The SLK is a lovely car but from a power/performance/speed point of view, I think the SL55 is ahead: Acceleration: 0 - 100km/h 4.7 vs 5.3sec Power: 476Hp vs 306Hp Torque: 700nM vs 370nM Fifth gear did a comparison on the SLK AMG and the SL55 AMG a while back with is worth watching: kzbin.info/www/bejne/gIS9iqpphpWVfZY Mike

[@mikeclinch1141]

Agree with a large part of what you say - disagree with your 3rd point above, I have charged both batteries without any disconnection and not had a problem - not sure why you should as you are just doing what the alternator would do - reviewed the dual battery wiring diagram for the r230 and still don't understand the rational for disconnection??? Maybe if you had a faulty charger can't think of any other reason??

[@MikesMercsandothercars]

Thanks for your comment. On page 375 of the Mercedes handbook which comes with the car , it states " Always disconnect the battery for electrical consumers in the boot first - even if you only wish to charge the starter battery. Otherwise the vehicle's electronic system may be damaged" Alternators are designed to maintain batteries that are near a full state of charge, not recharge deeply-discharged batteries. If your consumer or starter battery is flat, you should first disconnect it (see page 376) and take it out the car and charge it...according to Mercedes. I think one of the biggest reasons for the BCM failing is that some owners constantly drive their cars with a low/flat consumer battery resulting in MUCH higher current going through the BCM for longer periods of time than was originally envisaged. Mike

[@steveww07]

@@MikesMercsandothercars my home charger throws 10A MAX during dead battery charging. Can't see how that would damage any electronics considering alternators put out 10x that. I think Merc was just being extra cautious.

[@MikesMercsandothercars]

@@steveww07 I agree that 10 A to a battery directly is negligible......but when you put 10A to sensitive electronics, that is when the damage is potentially done. Call me cautious but if my SL55 has stood for weeks without being used to the extent that the battery has fallen to below 11.8v, I just take the consumer battery out and charge it. Mike

[@steveww07]

@@MikesMercsandothercars explain how a charger set to 10a max could do any more damage to sensitive electronics then an alternator. If anything the charger is “smarter” then the alternator by a long shot. I will however say that putting a charger on “jump start” mode may not be good, but I can’t confirm that.

[@MikesMercsandothercars]

@@steveww07 OK....here is my take for what it is worth: 1. In the R230 there are several modules connected even when the ignition is off. 2. There is a difference between a car battery charger and a car battery maintainer. 3. There can be a huge difference between car battery chargers in terms of their charging characteristics. 4. The Consumer battery in the R230 is an AGM battery and needs to be charged (as opposed to maintained) with an AGM charging profile. 5. The BCM is actually quite a smart DC to DC converter with all sorts of regulating inputs such as temperature etc In answer to your question..... The current output from a car alternator is regulated before it connects to the Battery Control Module and consumer battery eg the voltage regulator irons out any voltage spikes. If you connect a battery charger (as opposed to a battery maintainer) directly to the consumer battery is is quite possible there will be a voltage spike. The battery control module has electronics within it to smooth out and dissipate any potential voltage spikes. If you think of the electronics within the BCM as armour, then you can imagine that repeated blows (eg voltage spikes) can weaken the armour to the point that it eventually fails. Although the alternator on a car may be rated for 50-100amps, the alternator only actually puts out approx 5amps at idle assuming you are not running power hungry features. My degree in electronic engineering tells me that running a constant 10amps to a electronic circuitry which is designed to run on less current could shorten the life of certain components. As an example, red lining an engine occasionally, wont break it BUT driving up the motorway in 2nd gear as opposed to 4th probably wont help the life of your engine. Having said all of that, trickle charging an R230 with a Mercedes designed/recommended CTek is probably absolutely fine. Over and out. Mike

[@stefanvrabie6427]

pre-facelift w211 (E-Klass) had the SAME battery setup... not unique to the r230

[@MikesMercsandothercars]

Thanks for your comment. Sadly the W211 uses a different battery control module...which is a shame because they are a fraction of the price of the module in the R230 (£500 -£1000 used!) Mike

[@Mathematchit]

What was the first you did when you purchase your SL55, and don't tell me you inherited it from your grand-father.

[@MikesMercsandothercars]

My first car ever was the silver R107 SL which is currently up on my ramp. I paid £6000 thinking I had bough a bargain....but ended up quickly spending another £6000 to sort out the rust issues. The silver AMG was purchased new by a friend of mine. He had just been made a partner in a consultancy firm and decided to celebrate with a new Mercedes which cost just under £100,000....I always liked the look and styling of that car and told him I would be interested in buying it if he ever decided to sell it. Mike

[@Mathematchit]

@@MikesMercsandothercars What a way to celebrate, it's 2024 now and the SL55 is around $20K, what should i know about this car, i really need to be sure.

[@MikesMercsandothercars]

Are you planning to buy a SL55? If so, the most important thing to remember is that is is a complicated car and things will need fixing...or at very least maintaining. Mike