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SL500 (R230) batteries

Discussion in 'Electrics, Vacuum, Ignition and ECU' started by BiKenG, Nov 24, 2012.

  1. BiKenG

    BiKenG Active Member

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    Location:
    Surrey
    Your Mercedes:
    SL500/2007/5.3L
    I want to connect a couple of 'smart' chargers (CTEK) to my SL over the winter but could do with some advice/help:-

    Which battery is which? I.e. which is the starter battery and which the AUX (or whatever the other one is called)? I think they are front and rear respectively, but would appreciate confirmation.

    Any suggestions as to a connection in the engine compartment that could be used to connect to (and charge) the rear battery? Are any/all of the fuses from the rear battery?

    Is it possible to download a wiring digram from somewhere? With that I could probably work it all out. :)

    Hope someone can enlighten me with answers to the above.
     
  2. Fleetwood

    Fleetwood Senior Member

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    Horsham, West Sussex
    Your Mercedes:
    2005. SL350
    The front one is the starter battery

    The rear is the aux battery
     
  3. mikestrivens

    mikestrivens Senior Member

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    Your Mercedes:
    1995 W124 320TE, 1998 R129 SL500, 2016 Triumph Tiger 800 XCx
    As above. Put the CTEK on the rear battery. The front battery is only used for starting the car and serves no other function. Do take it for a run on dry sunny days to get all the lubricants circulation. This is especially important for aircon systems as the seals can dry out from lack of use.
     
  4. OP
    BiKenG

    BiKenG Active Member

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    Your Mercedes:
    SL500/2007/5.3L
    Thanks for that, at least I was correct about the batteries.

    But what connection can I use in the engine compartment from the rear battery? Would I be correct in thinking that all the fuses are from the rear aux battery? Since the front one is starting only, I can't think of any reason why there would be any fuses required, so the entire fuse box is surely just from the rear battery. In which case, I could add a connection for a charger there, or is there any better place in the front to connect to the rear battery?

    Is it possible to obtain a wiring diagram from somewhere?
     
  5. mikestrivens

    mikestrivens Senior Member

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    Your Mercedes:
    1995 W124 320TE, 1998 R129 SL500, 2016 Triumph Tiger 800 XCx
    Why not just connect directly to the battery. The CTEKs come with the appropriate leads to do this.
     
  6. Richard Hinds

    Richard Hinds Senior Member

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    Essex
    Your Mercedes:
    SL350, 2007
    I've got a CTEK charger, and it came with a short length of lead, which can be connected directly (and permanently) to either battery. (Mine's on the battery in the boot). This short length of lead terminates in a special two pin plug, and the output lead from the CTEK and then be "plugged in" to the battery when required.
    When the SL350 is not in use, I leave the CTEK "plug connected" to the rear battery, with the boot lid closed, and the CTEK outside the car, connected to the mains. The boot lid rubber seal easily accomodates the output lead from the CTEK.
    Every now and then I put the CTEK on the front battery, (using the second provided lead, which has croc clips) just to keep it topped up.

    Hope this helps!
     
  7. Fleetwood

    Fleetwood Senior Member

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    Your Mercedes:
    2005. SL350
    What CTEK charger are you using as need to get one for my car

    I've looked on their web site but there are far to many to choose from !
     
  8. SL55 Mark

    SL55 Mark Senior Member

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    Your Mercedes:
    2004 SL55 AMG
    Dear BiKen. I am a new R230 owner, and share your confusion. To answer your questions in turn.

    "But what connection can I use in the engine compartment from the rear battery? "

    None. There is no need. You can connect a charger directly to the rear battery to charge it.

    Both the small front starter battery and the large rear consumer battery charge from the alternator. It's a really good system. If you drain the main battery, there's always a spare to start the car. Once the car starts, you can recharge the main battery.

    "Would I be correct in thinking that all the fuses are from the rear aux battery? "


    Yes. Pretty much everything is powered from the rear battery, including lights, wipers, seats, and the vacuum system which powers roof, central locking, etc.

    "Since the front one is starting only, I can't think of any reason why there would be any fuses required, so the entire fuse box is surely just from the rear battery. In which case, I could add a connection for a charger there, or is there any better place in the front to connect to the rear battery?"

    There are three main fuse boxes, with other random fuses scattered about. It is true most of the systems the fuses protect are powered by the rear consumer battery. That is indeed the best place to connect a trickle charger to.

    "Is it possible to obtain a wiring diagram from somewhere?"

    I am looking into this. Because of copyright issues, the only source of up to date wiring diagrams for the R230 appears to be Mercedes own website, accessible through membership of an official Mercedes Benz Club. There are also CDs available on eBay, but as usual, it is a case of "caveat emptor"
     
  9. OP
    BiKenG

    BiKenG Active Member

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    Your Mercedes:
    SL500/2007/5.3L
    OK, a couple more points.

    CTEK recommend the MXS 3.6 or the MXS 5.0 for a car and that makes sense to me. I tried a motorcycle one but it never got to 'max' for the rear battery as I suspect it was losing charge about as fast as it was being replenished. Bike chargers/tenders/optimisers have very low output capability.

    I'm going to use a 3.6 for the front and a 5.0 for the rear as that makes sense to me. I'm not going to rely on a single one and have to remember to switch it over occasionally because I won't. I'll forget and since a replacement battery is about twice the cost of another CTEK...

    I tried moving a single charger around different bikes, but after having to replace a couple of batteries due to my forgetfulness, I realised the cheaper approach was an optimiser for each battery.

    Why not connect to the battery in the rear? Because I don't want to have leads trailing into each end of the car. I can hang both chargers from the ceiling at the front with no wires lying on the floor in danger of being tripped over. But for that to work, I need to be able to connect to the rear battery from the front engine compartment and it looks like I can. So I'll have the CTEK connectors both permanently installed under the bonnet/hood available for relatively quick connection.

    I'm not sure of the battery disconnect and connect procedure. One should be disconnected first? I guess what I need to know is can I simply disconnect the front battery (leaving the rear one connected)? My understanding is that this ought to be OK and in which case I can use that to confirm that any connection I make at the front really is to the rear battery by simply checking for 12v at the intended connection point.

    I've never understood why manufacturers make it so difficult to obtain information about their products. Why can't MB simply offer manuals and wiring diagrams etc for download over the 'Net. It won't cost them sales and will keep those customers who want that level of technical information happy instead of simply ****ing them off - as happens now.

    Surely someone here has this sort of info?
     
  10. SL55 Mark

    SL55 Mark Senior Member

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    Your Mercedes:
    2004 SL55 AMG
    The front battery doesn't drain. The rear one does. Don't bother with the front. As long as it is in good condition you'll be fine.

    Just charge the rear. There is no need to disconnect either battery. Just observe polarity. The owners manual covers this.

    You need a charger that is compatible with an AGM battery to charge the consumer battery, otherwise you may cook it.
     
    Last edited: Nov 25, 2012
  11. OP
    BiKenG

    BiKenG Active Member

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    Your Mercedes:
    SL500/2007/5.3L
    All batteries lose charge when stored. A charger is less than half the price of a battery. I'll fit a charger to both. :)

    Missing the point. I want to disconnect the front only while checking for a feed to the rear, then it can be re-connected. Just seems the simplest way to determine that a connection under the bonnet really is to the rear. Otherwise I won't know for sure that any connection I make will really be to the rear. If a terminal shows 12v, er which battery is that from. But if the front is disconnected, then I KNOW.

    Not come across a tender/optimiser that won't handle those. I don't think there's any real difference. The most important point to remember is it must be a genuine optimiser and NOT just a continuous trickle charger. I mentioned that I'll be using CTEKs and I think they have those points covered.

    But that still leaves the question of disconnection procedure. Which one first? Can I simply disconnect the front then re-connect it again without disturbing the rear?
     
  12. carnut13

    carnut13 Senior Member

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    Nr Sherborne, Dorset
    Your Mercedes:
    R231 SL400 & Audi A1 Sport
    Having bought a second car, the SL is now used less frequently. As a result ( after nearly 10 years of trouble free aux battery issues) I now have for the first time a notification of low aux battery....having done a search on this forum it seems I now need a CTEX to trickle charge the rear battery although the consumers come back on after about a 1 mile run.Should I stick with just a short run (5 miles to the shops) every 3/4 weeks with all the benefits that gives the car as a whole, or buy a charger?

    Am I correct in thinking the best model is the MXS5.0? If so does anyone know the cheapest place to buy it?

    As I have a normal battery charger for the front battery if needed would the cheaper MXS3.6 do the job on the rear?
     
  13. Smacsor

    Smacsor Senior Member

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    Bristol, UK
    Your Mercedes:
    2013 C250 CDI AMG Sport Plus; 2011 C220 CDI Blueefficiency 125 Edition - SOLD; R230 SL500 - SOLD
    I don't use my SL500 that much and regularly get the notification. But as you say, a couple of miles and its gone and as long as I do the odd hour drive, it's fine for a couple of weeks.

    I've also got a ctek 5.0 but don't use it that much. I'm sure the cheaper one would be fine, just take a bit longer to reach full charge? Mine takes about 5 hours to go from the point where the notification comes on to full charge.

    Simon
     
  14. OP
    BiKenG

    BiKenG Active Member

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    Your Mercedes:
    SL500/2007/5.3L
    Cheapest CTEK I could find:-

    http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=160927753460&ssPageName=ADME:L:OC:GB:3160

    that's item no. 160927753460

    Taking a car for short runs every 4 weeks or so is likely to be doing more damage than letting it stand - except for the batteries. Contrary to popular opinion, leaving a car to stand still causes no harm, whereas actually using it causes wear and in the worst case when just warming it up you create a lot of condensation inside the engine which then does nasty things, unless the car is truly up to full temperature. Something a short run to the shops is unlikely to do.

    Put a battery optimiser/tender on it to look after the battery and then just leave it alone - resist the temptation to start it up occasionally.

    Only other concern is to keep the tyre pressures up. Letting them go flat won't do them any good.
     
  15. carnut13

    carnut13 Senior Member

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    Your Mercedes:
    R231 SL400 & Audi A1 Sport
    Thanks

    Thats 1 all so far...any others with a view?:lol:
     
  16. Clkrichard

    Clkrichard Senior Member

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    Location:
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    Your Mercedes:
    CLK 320 Cabriolet 2004, R 230 SL 500 2005, new A class AMG Sport.
    I have a CTEK 3.6 with the lead permanently wired into the rear battery and simply connect the charger when the car is in the garage. I dont even fully close the botlid.
    I see no need to charge the larger starter battery up front.
    I bought my charger on Amazon.
     
  17. mikestrivens

    mikestrivens Senior Member

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    Your Mercedes:
    1995 W124 320TE, 1998 R129 SL500, 2016 Triumph Tiger 800 XCx
    As above, either take it for a decent drive to get it fully warmed up or don't bother. Just put the CTEK on, pump the tyres to over 40 psi and leave. But these cars do work better if used and fluids etc circulated, especially the aircon, on a regular basis. I tend to take mine out for a good run, around 40 miles mix of motorway and windy peak district roads, on nice dry winter days.
     
  18. OP
    BiKenG

    BiKenG Active Member

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    I forgot to mention how I connected to the batteries:-

    With the hood/bonnet up it's easy to see the front/starter battery and I have a CTEK lead permanently connected to that so it's easy to attach and detach the charger. But I didn't want to have to open the boot as well each time and connect a separate charger there, also because connecting to the mains at that end is more problematic.

    So I checked the fuse box (in the engine compartment, in front of the driver, opposite side to the front battery) and there's a spare relay socket not being used, but one of the connections is a 12v battery feed from the rear battery.

    A quick mod to put a terminal on the CTEK +ve lead and I have another CTEK socket, up front, permanently wired to the rear battery. So with 2 CTEKs tied together, back to back, hanging from the ceiling just in front of the car, there's a charging lead that runs up each side of the engine and the batteries are both being maintained in tip top condition for as long as the car sits there:)

    It's easy to position the leads so that the bonnet can be closed. I leave it on the 'catch' so I don't have to get in the car to raise it and disconnecting the chargers is a job that takes only seconds, yet they are there ready and waiting when I next need to park it up for a while.

    It's also obvious when sitting in the car that there are wired connections to it as you can see them dangling from the ceiling in front of you and hence I'm unlikely to hop in and drive off while still connected. However, if someone were to do that, the CTEK connectors come apart before damaging anything else.

    This is my first winter with this car, but I'm pleased with this set up and see no reason to have to change it for next winter.
     
  19. carnut13

    carnut13 Senior Member

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    Your Mercedes:
    R231 SL400 & Audi A1 Sport
  20. Richard Hinds

    Richard Hinds Senior Member

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    Your Mercedes:
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    Wow-what a great set of information! I'm busy printing it off as I'm typing this reply.
    Thanks very much for passing on the link. Please post up any more such "golden snippets" for us R230 owners!

    Richard Hinds
     

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