Hey guys…it’s time to put the old S550 away for the winter. I have my late father’s W221 which was delivered in December 06…so it’s a first edition 221 with the large consumer batter behind the back seat in the trunk. I have a MB CTEK charger/maintainer which I bought from the dealership. I spoke to three different techs at three different dealerships and they all told me to just connect the CTEK unit directly to the start battery and that that would maintain the system while in storage. I’ve heard many different views on this…with lots of folks saying that this technique will not charge/maintain the consumer battery at all. Just curious if any of you have any experience with this? Thanks!

 

We have a CTEK too but a different model. It's been ages literally since I used it but as far, I remember, I was just connecting the cables and select AUTO mode. The device was doing the rest of the job for me. The image you posted shows current status of the battery charging and it suggests to me that your battery is in good condition assuming it skipped the level of indicators faster than usual

 

there is a brain that works out which battery gets what from the alternator - I have ONLY ever trickle charged the car via the rear - the seal is so thick a mains extension cable easily fits (snug it at the gap by the tail light and the cable is above the boot lids lowest point) and thus you can close and lock the car with the charger connected. Its seems to keep both batteries happy and I've done it like this for 8 years

early twin battery cars - when pushing big current at the car for long diagnostics or programming sessions - you do not connect the positive to either battery terminal

one goes to the front battery earth and the other goes to a specific positive terminal of the front fuse link board under the cover beside the battery
you should never connect direct to both battery terminals - the car can't correctly measure the back ground current drain

 

Thanks BOTUS…someone sent me this pic…so if I connect the CTEK + lead to the post indicated and then the other to earth will this maintain both batteries or just the large rear consumer battery? Thanks for your input!

 

there seems to be at least three different set ups

you don't want to get this wrong - two PDF's on this site are both not what i have in my car

under the bonnet - on mine I have this pre fuse box 2215400850 under an 8" long black plastic cover beside the battery - the positive connection for your charger fits to one that's a lot taller than all the other posts - the one with the unthreaded part and the one furthest forward (nearer the headlight - opposite end to the normal fuses) as per these pictures - but sits with the posts straight up in the car. The other lead goes to the negative battery terminal - it should maintain the charge to both batteries

but then the bonnet has to be open and you can't lock the car - hence why I sorted a solution for charging when adding the missing cigarette lighter socket they need in the boot

 

Yes…looks like the same as mine. I’ve connected the positive to the front (tallest) post and the negative to the negative terminal on the start battery. Just curious…will this charge both the start and the consumer battery or does it bypass the start battery and only charge the consumer?

 

I just finished editing my post (plus nicer pictures) - its supposed to keep both batteries happy

 

Here is my set up…I’m able to run the wire out near the windshield and close the bonnet. The car is also in my garage so I can leave it unlocked. Thank for all your help! I really wanted to ensure that consumer battery (which is quite pricey to replace) was in good shape in the spring! Cheers

 

looks odd on the wrong side of the car

 

Ha…yes I’ll bet. I’ve never had the opportunity to drive anything but left hand drive cars here in Canada…and my international rentals have all been in countries that are also left hand drive. Every once and while you see right hand drive vehicles that folks have imported from the UK and other commonwealth countries. Would love to try it one day!

 

its easier than you might think - except three main bits

the really dodgy stuff it turning left out of a junction - flipping dangerous - particularity at a T junction on to a high speed / really busy main road.... you naturally look the wrong way and for the wrong lane (so its easy to miss something) !!!!
parallel parking (madness),
coming off dutch roundabout at speed where the inside rear tends to scuff the kerb (a lot)

and manual changes with wrong hand... this is quite odd (if right handed) once you learn to do it all with you left hand.... you'd think it easier to swap to the wrong side - as I then change with your right and more dextrous hand - buts its actually everything else about which gear and the road conditions making you have to change that required so much attention you forget how to change anyway

1/3 of the world drives on the correct side - main ones

Japan
South Africa and Bostwana
Australia and New Zealand
India
UK and Ireland

some evidence - on narrow roads with horse drawn carriages the "driver" sits away from the side, so his whip hand doesn't tangle in the trees and shrubs at the side of the road ... so you drive on the left
napoleon was left handed. you guys only do it wrong as the French encouraged everyone to protest against former britsh colonies

 

Lol…love it! right or wrong all I know is that now you’ve pointed it out shifting with my left hand would definitely take some time to get used too! I grew up driving standards in the 80s…VW bug, scirocco, Jetta GLI then a Jeep Wrangler…the first standard I ever drove was a three in tree. Standards seem to disappearing sadly on this side of the pond.

 

Mine's a 2010 with a single battery but since my owners manual details how to attach a battery charger, I expect yours does too.

 

Sadly the early 221 manual that came with the car only says to speak to your local MB dealer regarding how to properly maintain your batteries when storing the vehicle. All the techs I spoke to said to connect the maintainer to the start battery but I have since learned that this doesn’t give the large consumer battery any charge. Think I’ve got it figured out now.

 

I'm a dealer for Lithium ion batteries that have around 2000 cranking amps and tons and tons of reserve time that sit at 13.2 volts instead of 12. This means you don't need a tender either, and it also has a built in jump start cell, so you will never need jumped.. You also get a healthy weight drop from about 50 lbs from the stock battery to 15 lbs with the lithium battery. I'd be willing to help you guys out if you want to go this route. PM me.

 

Just DC the battery. You don't need anything at all.