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Discussion Starter #1
Wife left the key in the on position for several hours--now the battery is almost dead. The manual for the car says I have to disconnect the battery before charging. Is this true? I am aware that i have to keep doors or windows open so no explosive gas build up--but do i really have to disconnect the battery?
I've never done this on any of my other vehicle, and would rather not have to reset everything when i'm done....
Ben
 

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What kind of charger you have? With a good one you don't have to worry about disconnecting the battery for charging, but don't leave the key in the ignition.
You can hook up the charger to jumping post under the hood.
 

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The 1st thing to understand is that your kye MUST be out of the ignition on hookup, the 2nd thing you need to understand is that if current is interupted from the battery, the woners manual will spell out the necessary resetting procedures after the battery is reconnected.

Good luck buddy.
 

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What kind of charger you have? With a good one you don't have to worry about disconnecting the battery for charging, but don't leave the key in the ignition.
You can hook up the charger to jumping post under the hood.
I agree, my friend with the MB garage have a really good charger on wheels and if a car goes flat they never disconnect the battery.
Me with my very old little charger I always disconnect on MB but old Fords etc don't bother.
As fabbrisd1 said, take the key out and resetting after is a nothing job.
 

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Discussion Starter #5
I have a good vector "smart" charger. I can leave it all night and not worry about the battery being overcharged. I'd love to get this done so We both have cars in the morning.
Can i use the connections under the hood, or do i have to go under the seat?
Thanks guys..
 

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I recently charged my battery as it was reading at %74 charge. Took about 6 hours to bring it back up to %100, I also added water and connected the charger on the battery terminals.
 

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Discussion Starter #9
thanks everyone for your help in this little "emergency". Battery is charging (from the terminals under the hood). Should be 100 percent by morning.
Goodnight.
 

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What kind of charger you have? With a good one you don't have to worry about disconnecting the battery for charging, but don't leave the key in the ignition.
You can hook up the charger to jumping post under the hood.
x2. not sure why mercedes say not to charge this way, but as long as it is a decent charger, which amounts to almost any you can buy today, shouldn't be an issue.
 

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i don't think one should blindly charge the battery using the convenient charging points
beneath the hood without at least checking the battery's fluid levels. there is always a
chance that the electrolyte may have cooked off enough to expose the tops of the plates.
it only takes a few minutes or so to pop the caps and verify that the electrolyte is just
below the bottom of the filler tube.
 

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I am not sure how many members would notice electrolyte level on the battery mounted under the seat.
As far as I know all W210 are equipped with maintenance free batteries, that usually don't even have plugs for adding distillate water to them.
I think MB recommendation for disconnecting the battery for charging come from liability issues. The process is not idiot-proof and since the popular saying is "bigger is better" lot of owners would not hesitate to hook up 30, or even 50 amp chargers to the batteries.
In this case it is opposite. Optimal would be 2 amps, while generally max charging current is 10% of battery capacity or 10 amp for this model.
Older non-automatic chargers would go as high as 16 volts, what might mess some electronics (even with key off some stuff still works on the car) but left for too long would boil the battery with potential for blowing it up.
 

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I am not sure how many members would notice electrolyte level on the battery mounted under the seat.
As far as I know all W210 are equipped with maintenance free batteries, that usually don't even have plugs for adding distillate water to them.
I think MB recommendation for disconnecting the battery for charging come from liability issues. The process is not idiot-proof and since the popular saying is "bigger is better" lot of owners would not hesitate to hook up 30, or even 50 amp chargers to the batteries.
In this case it is opposite. Optimal would be 2 amps, while generally max charging current is 10% of battery capacity or 10 amp for this model.
my original battery and replacement battery, both mercedes OEM are flooded cell batteries with caps to check the water level. Manual recomends checking the water level. Unlike most flooded cell batteries, they have an o ring seal on the caps and then there is a tube leading to underneath the car to vent hydrogen and any acid vapors. Since the caps are sealed, t and the battery chemistry is similar to a "maintenance free" battery , they loose little if any water over time.

Keeping the max charging current to C/10 is a good idea for maximum life on typical starting batteries if you want maximum life.
 

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in both my mb batteries you can remove the plugs and add distilled water. haven't checked them in years though, hopefully sometime this week and maybe post a pic.
 

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i agree....the caution goes both ways. if you see a well sealed 'maintenance free'
battery, leave it alone. same goes for AGM or gell battery (dont even think of adding
water). but there many of us regulars here who will shop cautiously and continue
to purchase flooded cell, Interstate/AutoZone, et al brands for $75+-

I should have typed with more precision
 

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That is a surprise if those are not maintenance free.
Caps don't necessary indicate that you should open them. Our ML320 had battery mounted under the hood with big caps on cells, yet it was maintenance free. We never opened the caps in over 12 years the battery lasted.
 

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I remember seeing the battery maintenance on the ASSYST sheet, checked it again and "check and correct battery fluid level" is both part of Service A and B unless it is an AGM battery.
First time I checked it myself after 8 years of dealer maintenance prior to 2009, it was evident that the caps on the battery was opened.
Found the fluid checking precedure and ended up adding distilled water prior to charging and I did use the slow charge option.
 

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I don't in any way mean to hijack this thread, but I have a a quick question. My battery just died. I know you're not suppossed to do old fashioned jumps, but I don't have a charger. So..options? Tha manual says to jump charge but I haven't seen it discussed so idk if it's good/bad?
 

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So are people charging the battery via the underhood lug?

Seems sensible to me - can't easily understand why it wouldn't be possible, what kind of funky electronics are set up in a w210, that, for example, even my 2011BMW, which has a trunk mounted battery, doesn't have.

Unless it is liability against someone installing with no vent tube?
 
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