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1995 W140 S280
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Discussion Starter #1 (Edited)
Well, so here it is, my first (self inflicted) car problem.

Last week I parked the car and put a new car cover on it (garage is dusty). Two things weren't proper; interior light was on, and the driver's door wasn't fully shut. Both were not spotted due to the car cover. It was then locked from the remote.

7 days later (today) I returned to find the battery dead as a doornail. The only saving grace was the half closed driver's door which at least let me into the car but the trunk has remained stubbornly shut - cracked the plastic key handle trying to open it. No soft-close on this car.

Have read through all the "flat battery" related threads on here and tried to find the pax side (RHD here) terminal under the carpet but wasn't able to find it.

Am now waiting for my mech to stop by who told me over the phone since I can get in and thus pop the hood, it can be jumped from the alternator (?!) Paying a pretty penny for this though.

Three questions right now are:
1. How long ago do you guys think the battery died with an interior light on?
2. How much damage has been done to my battery? (Sulfation or otherwise)
3. How much damage will my alternator take if being used to start the car and charge the battery?
 

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Outstanding Contributor
450slc5.0cab 280sl5sp 280se4.5 500seAMG +250seStkW108 350sl4spdX3 500secEuro
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I take the battery out of my 1993 300se and lock it up all the time. Are you both turning the key and pressing the button in?


Some other concepts:
  • 12 v in the cigarette lighter with the key on
  • The big battery cable should go directly to the starter. You could hook a charger up to that (and a ground).
The trunk mount battery 107’s I work on all the time have a hot service point in the engine bay. I never had to look for one on my w140.



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1995 W140 S280
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58 Posts
Discussion Starter #3
Okay some updates.
Mech took off the air box, hooked a battery to the alternator, which powered everything up, set the alarms off and all. With this we could open the boot (lock is faulty, it turns out), then hooked the battery up the normal way and let the car run at 2500rpm for about 5 minutes.

Despite this, the battery is still very near dead (despite being only 18 months old). Windows cannot go up smoothly, will only do so about an inch at a time, and the dash lights flicker each time I hit the button.

Drove it 30km for about an hour and only just stopped the engine. Not sure if it will start again later but there's a second car where I'm presently at.

Is trickle charging still an option to save this battery or do I need to buy a new one?
 

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1995 W140 S280
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Discussion Starter #4
Well, my Sunday just got a whole lot worse. The car hesitated a bit but started up fine for the return trip. However not more than a km from my destination, in slow traffic, it just suddenly stopped dead. Couldn't be restarted (and to make matters worse the plastic bit on the key finally broke so I had to improvise with a ratchet). Even after managing to borrow a fellow motorist's battery - he had the smaller "normal" sized one - the engine wouldn't crank at all.

Awaiting roadside assistance while reporting myself on Waze. :cautious:
 

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1995 W140 S280
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Discussion Starter #6
Happy ending...sorta. So after the helpful motorist left and I had sat quietly for a couple minutes, I realized the shifter was in neutral - was just rolling to a stop in slow traffic right before the engine died. Major brain fart - incredibly stupid even - but I put it in Park, turned the key once more and she started right up. Should've noticed something was amiss when it didn't crank even though only the battery was low.

The only mystery left is how the engine could stall out all of a sudden. It did do the "RPM dips alarmingly and quickly recovers" once on my return trip but I chalked it up to the battery not being back up at normal charge levels. Drove 5 more minutes after that to my garage and locked it up - properly this time. Unfortunately I'll be out of town for another week so can only wait till then to find out what tantrum she'll throw next.
 

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450slc5.0cab 280sl5sp 280se4.5 500seAMG +250seStkW108 350sl4spdX3 500secEuro
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You drained every bit of power out of that battery. You are lucky it starts anything at all. Normally you need 24 hours of low amp charging to bring the battery back to life.

It is possible that your alternator is not charging too.

Go buy a $40-50 automatic battery charger at your local parts store or Home Depot and put it on the battery with the 2-3 Amp setting, and check it out when you return from your trip.

To be safe from the battery boiling over, put it on the floor instead of leaving it in the car.

Is it an AGM battery or standard?


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1999 S600 & 1999 S500
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Happy ending...sorta. So after the helpful motorist left and I had sat quietly for a couple minutes, I realized the shifter was in neutral - was just rolling to a stop in slow traffic right before the engine died. Major brain fart - incredibly stupid even - but I put it in Park, turned the key once more and she started right up. Should've noticed something was amiss when it didn't crank even though only the battery was low.

Been there , done that!
 

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1995 W140 S280
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Discussion Starter #10 (Edited)
Update: was reading up on batteries here. Came across this from Merc-S600 and my heart damn near stopped.

Correct me if I'm wrong please - is this the "proper" battery-flat recovery scenario?
0. Do not jump the car with another car or battery - supposedly this also includes portable jumpstart packs
1. Disconnect battery using a specific proper procedure
2. Slow charge with a restorative/trickle charge (is 1A over several days a safe charge?)
3. Reinstall battery and start car
 

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97 S600 Coupe. Former 83 300D, 97 C230, 93 400E, 92 500SL, a few others
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I deal with battery drain in a rotating fashion on 3 of my cars when I pull them out of storage (all 3 are competely and totally dead after sitting 1-3 days and start and run fine after the battery is slow-charged).

The Strongway 800 amp jumpstarter from Northern Tool will start anything with one key turn the second after you hook it up. No BS. Don't mess with the stupid crap from Autozone/etc that Billy with the 12 year old's mustache will tell you "works great mane all you need." Then, at home, and if you have the garage space year-round, leave it on the Noco 3500 trickle charger. Has various modes, including a battery repair mode. Trust me, I went through 3 Interstate batteries on 3 cars needlessly, the problem wasn't the battery or alternator, it was the fact that once completely drained dead the only way to recover them without driving them 50 miles for 2 hours is to just use the right jumpstarter that has the JUICE, and then the right trickle charger to fill every cell back up while you sleep.
 

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1995 Mercedes S420, 1995 SL320, 2000 Land Rover Discovery II, 1985 Lotus Turbo Esprit
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Yeah it sounds like you destroyed that battery and you're not going to get it back without proper procedure (or a new battery). As will said above, if you really killed the battery the only way you're getting it back is a good trickle charge for a few hours at least. Once you resolve that, you can see if anything else is wrong, like your alternator.

After you recover/replace the battery (if it were me I'd just buy a new one), get yourself a multimeter and put it on the battery terminals with the car running to ensure it's getting the proper voltage. Should be 12 volts with the car off, a quick dip when the car is started, and then 13-14 volts with the car running.

I went through something similar and it turned out to be my alternator regulator. Not saying that's your problem for sure, but it's something to keep in mind if a recovered/replaced battery doesn't do it for you.
 

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2006 E320 CDI
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Having numerous cars, mowers and other toys, I use chargers called a "Battery Tender" to maintain batteries or charge them over time. The chargers switch to a "float" voltage when the battery is charged to keep them at charge when the car/toy isn't going to be used for some time. It monitors the battery and if/when it starts to drop in voltage due to some draw, it charges it again and then switches back to float when charged, repeating this process as needed. They come in various amperage outputs. I have them in 750 mA versions to 5 amp versions. They are not that much money and it saves expensive batteries. It will also tell you if your battery is toast or not when you hook it up. I use 5A versions for lead acid car batteries.
 

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1995 W140 S280
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Discussion Starter #14 (Edited)
Okay, I've ordered a 1A charger to help repair the battery however much it can. However as mine is an apartment parking garage, the battery will need to be removed and charged off-site, with the car being manually locked. Also just arrived is one of those USB chargers you plug into the cig lighter with a voltage readout, will check to see what that shows this weekend - if the car even unlocks or starts at all fingers crossed.
 

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1995 W140 S280
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Discussion Starter #15
Still been reading up on electrical stuff and alternators etc, and had another "oh crap" moment. o_O
So you guys remember the key sort of broke, well after turning it to position 0, because I was exhausted and also not in perfectly clear thought, I left it in there thinking I'd be back with a plier to get it out. Granted, with a bit of pain and effort I could have extracted with my fingers but alas, I didn't.

Now, some people are saying "some cars" detect the key in pos 0 and don't go fully off - bad news. So I dug out the e manual and it says
2610925



Jesus H. Does anyone know if the 95 140 is one of "those" cars that doesn't have a dumb lock? I might have to urgently arrange for someone to go tend to it before my return if that is the case.
 

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1994 S600 Coupe, 1995 S600 Coupe
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If you pull the key out, then put it back in, you are ok, as long as you don't turn it. If you left the key in the off position, but didn't pull it out, you leave some systems activated, such as the radio.

Jon
 

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1995 W140 S280
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Discussion Starter #17
Yeah it wasn't pulled out due to broken handle. I did manually turn off the radio before parking the car (hold power button).
Does that put the radio into a state that will at least last a week on a normal battery?
 

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1994 S600 Coupe, 1995 S600 Coupe
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I don't think it's just the radio. That was just an example.

Whenever you leave the car for more than a few days, put a float charger on it.

Jon
 

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1995 W140 S280
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Discussion Starter #19 (Edited)
I couldn't get anyone to tend to Diana yesterday so may have to be prepared to find the battery discharged (again) this Saturday.
However, this time I'll be bringing the original key and don't intend to call roadside. In order to unlock the boot from central locking via remote, the car needs power, which can apparently be provided using a "memory saver" device plugged into either the OBD-II or ciggy port. My car doesn't have the former, and it takes too long to order the device online. The below reportedly works with older/simpler cars, but I have not found information specific to the 140.

Can anyone confirm if connecting a 9V battery to the cig port and switching to Position 1 will not harm a 140 please?
 

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Discussion Starter #20
Updating this thread for posterity, in case this turns up in a search by anyone from the future.
For the short term, I consider this incident/event more or less closed.

1. Leaving the key in pos 0 will not drain the battery if your car is properly locked. At least after a week, it started right up.
2. I still do not know if you should connect a 9V battery to the cig port and turn the key to pos 1.
3. MB indie fixed my manual trunk lock for $10.

She starts and runs fine, 12.4 volts with engine off, ~13.5v with engine running, measured at the outlet with a cheap usb charger.
There is a recently-appeared "sudden stall" issue that may be related or just coincidental, but a separate thread for that would be more appropriate.

Have a pleasant week ahead everyone.
 
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