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How to properly charge a dead car battery

Dead Battery? Don’t worry; you can bring that battery back to life if you charge it properly. Jump-starting the car is not recommended on a wholly discharged battery unless you have to. Remember that jump-starting will run the car, but you risk damaging the battery. You can damage battery cells or make the battery not hold a charge as it should. A car battery can last 5 to 7 years; your battery should have a sticker with the date it was made on it.  If your battery is not over seven years old, don’t give up on it. I just had an 8-year-old Mercedes Benz  SLK Class parked for three months, and when I went to start it, there was no power. So here is what I did to get the car started.

First, there are two things you will need to bring a completely dead battery back to life.
1. You need time. At minimum one day, preferred two days.
2. A trickle charger.
A trickle charger will put a very slow charge on the battery and bring it back from the dead. Any of these chargers on Amazon will work; some cost only about $20, which is well worth it. All you need is a 1.5 or 2.0 Amp 12-volt charger.  If money is not an issue, you can get a charger and starter simultaneously. They cost a little bit more but allow you to do a 2.0 Amp slow charger, a fast 10amp charge, and a 75 amp or higher setting for jump-starting. Here are a few highly ranked ones on Amazon that work as chargers and starters.
If you try to charge a dead battery by jumping starting the car or putting a current over 10 amps on it you risk damaging the battery. Not even that, but if you have a battery that has terrible cells, it could even explode.

How to recharge a completely dead battery.

1. Find a charger. If you don’t have one, see this list. 
2. a. Remove the battery from the car.
2. b. Or if you want to leave the battery in the car, disconnect the negative terminal from the battery.
3. Connect the red  (+)positive cable from the charger to the positive terminal on the battery.
4. Connect the charger’s black (-) negative cable to the battery’s negative post.
5. Plug your charger into an outlet.
6. Let it charge for at least 24 hours. Check the battery in a few hours to ensure it’s not getting too hot.
The SLK battery I charged took two full days to charge, ultimately.
Note: If your battery is older than 7 or 8 years, you should replace it soon. Because there are a lot of electronics consumers in these luxury cars, they tend to be very sensitive to the battery voltage. When the battery doesn’t provide the voltage and current, you may notice strange malfunctions with systems such as the transmission, ECU, and airbag.

If your battery is old or you don’t want to even deal with charging a battery, you can quickly get a new battery on Amazon that will fit your Mercedes Benz. They are brand names; you can get the battery at your front door. Check out these highly-ranked batteries on Amazon that fit Mercedes-Benz cars.


If you have any questions or comments, feel free to comment below.


  1. Hello, thanks for the great advice. My car is a Mercedes 1999 SLK 230, and the charger is a 3A 12V Battery Tender. The car manual advises to disconnect the battery from electrical circuit before charging the battery. In one of your responses you mentioned that if the negative battery terminal is disconnected, no damage will occur to the electronics. Even if no damage occurs, do you know if some of the electronics would have to be reset?
    Thanks again 🙂

  2. There is a fault with my boot/trunk and its not opening, so I can’t access the battery. Is it possible to charge from the front compartment without disconnecting the negative on the battery itself? Thanks in advance!

  3. I’m having a trouble with my battery I bought this 2000 Mercedes Benz S430 over 200,000 miles at auction for $900 and so far it has not given me any trouble except that now is not starting I’m having trouble getting the battery to start the cigarette lighter doesn’t even work but those are mechanical things a few things are outdated on it because it’s 17 years old but I just need some guidance on what I need to do about the battery because it’s been frustrating trying to get it started I cannot afford a new battery I like to be able to get a reconditioned battery I can’t afford to go to Chesterfield Auto Parts to get a reconditioned battery for $75 and I’d like to be able to find out exactly what’s wrong with it I can’t afford to have somebody come here to look at it or I can’t even afford to have it towed somewhere for someone to look at it if there’s any way someone could help me figure out what’s going on I’m out here now feverishly trying to get it to start I’ve got a jumper box which seems to be doing okay it tries to start and then it stops and just can’t get there I’m wondering if the starter needs replacing or what’s really going on at this point

  4. Very good Website
    I’ve got Mercedes w221 s500 2011 model I’ve got issues coz I drive for 3-4 days and then stays in garage for 2-3 weeks when I try to start the battery isn’t strong enough to turn the engine over is it any charger that keeps the battery charged up or to recommend which one so I can leave in slow charge

  5. You say the battery can be charged while in the car, just disconnect negative side cable. What about positive side, does leaving the positive side connected while charging the battery not potentially harm the electronics in any way?

    • If you disconnect the negative, the car has no power. It doesn’t matter if the positive remains connected. You need both + and – to get power (current) to the car electronics.

  6. Thanks for the information. I performed the trickle charge for about 36 hrs on an 07 E350. Reinstalled the battery and so far seems to be working fine. I am sure a new battery is in the future but it was great to not have to buy it today.

  7. Great website! I came here because my S Class W320 started first time today when I moved it across the yard to wash it. It hadn’t been started for about 4 days but fired up perfectly. Key was then removed. About an hour or so later I went to move it back only to find it was EXACTLY like your video clip! I had no choice but to jump start it because it was blocking someone’s garage. It started fine and I moved it across the yard. A couple of hours later I went back to the car, remote locking worked fine, car fired up first time. I switched it off and started cleaning the interior. I then went to start it only to have the same problem! Can’t even lock it now. Can a battery really die that quickly???

    • It may not have been charged fully in the first place. Try charging it with a 2A or 4A 12 volt charger. If it still gives you problems then you need a new battery. Also if the battery has any damaged cells it won’t charge and may be the reason why you are having the problems described.

  8. I left my 2004 clk 320 in the garage for 5 months now. And when I came back from a long trip. It’s totally dead. And I’m sure the battery is past 8 years so new one needed for sure. I can’t change the battery myself because the way it mounts is hard to reach. Before I towe it to the shop. You think my car can still be save? Will it able to start and drive again. It was in perfect condition before I left. Only 110k on it

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