Battery drain
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Member
Joined: Nov 2019
Posts: 79
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w211 04 e220
Battery drain
So something that has never happened, yesterday evening,when I tried to unlock my car nothing happened,battery was DEAD,I opened car maybe 10 hrs before that everything was ok. took out the little key charged the battery one in the trunk.As soon as I plug the cable the 4 indicators started flashing(panic mode),which leads me to believe that something tripped it and drained the battery,still not sure.Checked the voltage was low 10.1,started car drove it,while driving it said around 13.8-13.9 voltage.When turned off right now it says 12.2 voltage,so I will check again in 5-6hrs voltage,what is the normal while the car is turned off,I guess around 12-12.2 right?Also I didn't lock the car and every light is off etc,so nothing can trip panic mode..
Last edited by Matteo Sukic; Jan 12, 2020 at 10:30 AM.
Junior Member
Joined: Dec 2014
Posts: 19
Likes: 4
2011 C300 4matic
Definitely have a drain somewhere.
12.6 volts is a fully charged battery, at 12.4V its considered 75% charged, at 12.2V its considered 50%. I would charge the battery fully on a battery charger with it disconnected from the car. Do you know how to check battery draw after to car goes to sleep?
12.6 volts is a fully charged battery, at 12.4V its considered 75% charged, at 12.2V its considered 50%. I would charge the battery fully on a battery charger with it disconnected from the car. Do you know how to check battery draw after to car goes to sleep?
Junior Member
Joined: Dec 2014
Posts: 19
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2011 C300 4matic
Well you have to have a multimeter or something with the ability to measure amps. They make one you can clamp on to the battery terminal and it will tell you, i just use a meter. To use the meter you disconnect negative cable and clamp one lead to the battery terminal and the other lead to the negative cable. This will reconnect the battery to the car. You then should make it think the trunk is shut and lock the car. It should go to sleep in like 20 minutes. Shouldnt have more than 50 miliamps being drawn. If you have more than that start pulling fuses. Everytime you pull a fuse it can "wake up" the car so you have to let it go back to sleep. There are lots of threads about this on here you can look at for ideas.
I had to do this on my 05 wagon. I had a bad audio gateway that wouldnt let they system go to sleep. Would kill the battery over night. Seat modules can do this as well as the alarm siren in the fender along with some other modules i cant think of right now.
I had to do this on my 05 wagon. I had a bad audio gateway that wouldnt let they system go to sleep. Would kill the battery over night. Seat modules can do this as well as the alarm siren in the fender along with some other modules i cant think of right now.
Thread Starter
Member
Joined: Nov 2019
Posts: 79
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w211 04 e220
Well you have to have a multimeter or something with the ability to measure amps. They make one you can clamp on to the battery terminal and it will tell you, i just use a meter. To use the meter you disconnect negative cable and clamp one lead to the battery terminal and the other lead to the negative cable. This will reconnect the battery to the car. You then should make it think the trunk is shut and lock the car. It should go to sleep in like 20 minutes. Shouldnt have more than 50 miliamps being drawn. If you have more than that start pulling fuses. Everytime you pull a fuse it can "wake up" the car so you have to let it go back to sleep. There are lots of threads about this on here you can look at for ideas.
I had to do this on my 05 wagon. I had a bad audio gateway that wouldnt let they system go to sleep. Would kill the battery over night. Seat modules can do this as well as the alarm siren in the fender along with some other modules i cant think of right now.
I had to do this on my 05 wagon. I had a bad audio gateway that wouldnt let they system go to sleep. Would kill the battery over night. Seat modules can do this as well as the alarm siren in the fender along with some other modules i cant think of right now.
Thread Starter
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Joined: Nov 2019
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w211 04 e220
Update on this morning all normal drove it parked rn opened door says brake workshop again low battery could it be that the sbc battery in front is bad and draining the on in the rear?also tested the alternator and the rear battery all is good didnt test the front one
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Joined: Dec 2014
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2011 C300 4matic
The aux battery for the sbc is isolated from the main battery by a relay when the ignition it turned off. It shouldnt drag the main battery down, doesnt mean it cant though if something is wrong. When you start the car it senses the sbc battery and if its below something like 12.4 volts it triggers that alert. How old is your aux battery?
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Thread Starter
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w211 04 e220
The aux battery for the sbc is isolated from the main battery by a relay when the ignition it turned off. It shouldnt drag the main battery down, doesnt mean it cant though if something is wrong. When you start the car it senses the sbc battery and if its below something like 12.4 volts it triggers that alert. How old is your aux battery?
Last edited by Matteo Sukic; Jan 14, 2020 at 06:46 AM.
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Thread Starter
Member
Joined: Nov 2019
Posts: 79
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w211 04 e220
my mechanic will come tomorrow to check again the batteries,and i will also do the check on battery drain,although he did it while checking the main battery we turned the car off and after few minutes he hooked up meter and all reading was like it should be
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2011 mercades e350 rwd
Add more grounds
I have a 2011 e350 when I start the car I get a consistent flow between 12.4 and 14.9 once driving its stay at a steady 12.3-12.6 once parked i can stay there forever. If i add a load the lights flicker and starts to kill the car. I have to open the door so it can activte the said OPPORTUNISTIC CHARGING and turn to the battery and " charge it". Now I add load. I use a 120 inverter at full capacity and the wattage screen fluctuates between 11.4 up to 14.5ish so that means it would be discharging the battery if I turn off the AC and I disconnected the loads it stays at a steady 13.3ish Voltz. My experience. I hear that disconnecting the LIN from the Alt stops the Rsam control from getting hit with 90 amps. Idk of true but would love to see tests. And how to remove said Lin cable. 🤔
Last edited by Vicmech; Oct 7, 2025 at 09:59 PM.
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Joined: Nov 2025
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From: California
2003 mercedes benz e500 w211
Did u fix the problem
I have a 2011 e350 when I start the car I get a consistent flow between 12.4 and 14.9 once driving its stay at a steady 12.3-12.6 once parked i can stay there forever. If i add a load the lights flicker and starts to kill the car. I have to open the door so it can activte the said OPPORTUNISTIC CHARGING and turn to the battery and " charge it". Now I add load. I use a 120 inverter at full capacity and the wattage screen fluctuates between 11.4 up to 14.5ish so that means it would be discharging the battery if I turn off the AC and I disconnected the loads it stays at a steady 13.3ish Voltz. My experience. I hear that disconnecting the LIN from the Alt stops the Rsam control from getting hit with 90 amps. Idk of true but would love to see tests. And how to remove said Lin cable. 🤔
Did u end up finding out the issue
