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Ok time for another "my battery has gone flat and now my slk wont start" thread!

2675 Views 26 Replies 10 Participants Last post by  tricolour
Similar story to some other threads on here:-

SLK55 AMG battery goes flat.

Battery charged and reinstalled - car wont start.

Turn the key to switch ignition on and everything lights up on the dash as it should.

Continue turning key to start the engine and everything electrical switches off and i mean everything!

Only way to get electrics back is to disconnect the battery and then reconnect it.

Based on the above i would assume its a blown fuse so checked following fuses:

Engine bay:


In the cabin:


All are ok so now i am out of ideas.

Could it be a relay?

Any guidance would be gratefully received.


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Did your battery go flat (I mean, really dead) any earlier? If so, then I would say: Take the battery to any car workshop and have it tested. Lead acid batteries will not survive if they go completely empty. If the battery is still okay, then it sounds indeed like a weird relays problem. Is the car completely dry? No moisture problems anywhere (not even in the boot/trunk)? Unlikely to be the cause, but just to take it off the list: Same problem with your spare key? Arjen.
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Is that your original battery from 2006? then it was probably made in 2005. then it is almost 11 years old?
it is the original battery.

However when i charged the battery i have a smart charger that charges the battery and then tests it.

I tried it a couple of times and the charger said the battery was "strong"
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i wonder if that smart charger can detect bad cell(s) or just measures the other cells as compensating. Bet a new battery solves all your problems
i wonder if that smart charger can detect bad cell(s) or just measures the other cells as compensating. Bet a new battery solves all your problems
Agree! When I bought my car, I had a cheapo battery in it. I immediately replaced it for an OEM one, but kept the cheapo as a spare for the winter (when the car is hybernated) or for hobby testing 12V components.
I have charged the cheapo a couple of times, and every time the CTEK trickle charger says it is fully charged after a day or so. The colour indicator on top of the battery also indicates it is "ready to use".
Yet.... within one day it is dead. :td: Hence, swap the battery a.s.a.p. (particularly now that the outside temps have dropped) and please report back.

I would recommend you to either buy an OEM battery at the dealership or a well-known brand like Varta.

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You can read about my recent problems that turned out to be a battery by searching "Instrument Cluster". I vote for a new battery.
New battery would be a good investment.
i'll pick one up in the morning and let you guys know what the result is!

Thanks for the feedback
Hi All
Can you try I a different battery off another car , just see if the car will start or do the same thing .Or use jump leads.


I had this happen on mine 2 years ago. Returned from a short plane trip and the car wouldn't turn over. Battery was fine. I towed it home and spent a lot of time looking on the net. I found a post (which I should have saved) that said to pull a fuse on the driver's side fuse box and replace. I did and the car started right up. Fuse wasn't blown. Problem is, I don't remember what fuse it was or what the circuit was. Hasn't failed since. If you know your battery is good, it's worth a shot though you'll have to pull all the fuses and put them back in. I'll keep searching for the post in the meantime. Good luck.
Erm thanks I guess but I already pulled fuse f36 in the cabin so I'm guessing that's the same one you pulled as it's the only one related to the starting system
Is that your original battery from 2006? then it was probably made in 2005. then it is almost 11 years old?
11yrs is quite a while for a battery.
if charged at least weekly, yes
Hey presto ?
Got new car battery? Did you do conductive testing on the new and the old battery?
Put new battery on and it worked.

I didn't carry out a back to back test of the two batteries I'm afraid.

What I would say that might help other members is that when I fitted the new battery the electrics died as with the old battery when I tried to fire it up but I noticed when I turned the key back around the electrics came back on (they didn't with the old battery) so tried again and again and again and on the 4th attempt it fired up. But the 3 times before the electrics died and came back on when the key was rotated back to its first position.

Not sure if that will help anyone else or not but thought I'd share it.

Car starts first time every time now
we told you so

synch windows
reset clock
You did Jeff but during the first 3 attempts to start it your name was mud ?

Window sync - my windows always do weird stuff after the battery has been disconnected. I find the way to fix it is shut doors lock the car and then press and hold the lock button on the key fob. After 5 seconds or so all the windows shut and then work perfectly after (drop and close with door open and shut and work perfectly off the buttons as well)

Clock - not bothered yet as installing new sound system so no doubt battery will be on and off a few times yet
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