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I would advise putting the CTEK back on it for up to 48 hours. Depending on the CTEK model you have, it should indicate that the battery is fully charged and the charger has entered the float mode. At that point, the voltage should be 13.6V. When you disconnect the CTEK, it should drop to around 13.0. If the CTEK can't get above 12.4 or so, the battery is bad. I really don't want to debate whether a bad aux battery can trigger this error. (If you recall, my position is that low voltage to the battery control module can raise spurious errors, but if you don't agree that's fine.) But, regardless of any other problem, If 48 hours on the CTEK doesn't reach float at 13.6 V, the battery is bad and should be replaced anyway.
First, I have a CTEK 3300.
I connected it to my trunk battery yesterday and today i can see that the charger is showing 'green' light, which means the battery is fully charged. It must be in "float mode", correct?
With the CTEK connected, (engine off) .... i measured the voltage and i saw that it was actually NOT stable. It was around 13.2V when i first connected the volt meter, and it was slowly going down. When it reached about 12.8V, the CTEK switched to charging mode, the voltage jumped up to 14 volts .... and after 10 seconds or so, CTEK went to green light again (float) and the voltage dropped to 13.5-7V and started to drop slowly.... back to 12.7V or so.... then CTEK kicked in again for 10 seconds.... and then the same sequence repeated.
Is this normal behavior with these CTEK chargers or this points to my battery being unhealthy?
I connected it to my trunk battery yesterday and today i can see that the charger is showing 'green' light, which means the battery is fully charged. It must be in "float mode", correct?
With the CTEK connected, (engine off) .... i measured the voltage and i saw that it was actually NOT stable. It was around 13.2V when i first connected the volt meter, and it was slowly going down. When it reached about 12.8V, the CTEK switched to charging mode, the voltage jumped up to 14 volts .... and after 10 seconds or so, CTEK went to green light again (float) and the voltage dropped to 13.5-7V and started to drop slowly.... back to 12.7V or so.... then CTEK kicked in again for 10 seconds.... and then the same sequence repeated.
Is this normal behavior with these CTEK chargers or this points to my battery being unhealthy?
No, it shouldn't be swinging that much that quickly. It sounds like you might have a current drain on the service (aux) battery. The important question is how low the voltage goes with the CTEK and engine both off in, say, 24 hours. 12.7 is ok but 12.4 isn't. So, starting at 12.7 how long does it take to drop, and to what does it drop? If it's as low as 12.4 or lower, you should check for current drain (put the meter in current/AMPs mode and CONNECT IT IN SERIES with the battery). Make sure your meter can read up to a few amperes. If your meter is not capable of reading amps (as opposed to milliamps) or you're not comfortable hooking it up in series with the battery, it might be time for a pro to check out what's happening with your service battery circuit.
I was out of town since last Friday.
The car was parked in the garage, locked, for good 5-6 days.
Came back today, measured the rear battery voltage and i got 12.25-12.30Volts, with the engine off.
Do these numbers look OK for an AGM battery, sitting in SL for 5 days?
I was out of town since last Friday.
The car was parked in the garage, locked, for good 5-6 days.
Came back today, measured the rear battery voltage and i got 12.25-12.30Volts, with the engine off.
Do these numbers look OK for an AGM battery, sitting in SL for 5 days?
Thanks!
It'as not clear to me, if these 5 day's are with the CTEK connected or disconnected ?
It'as not clear to me, if these 5 day's are with the CTEK connected or disconnected ?
Sorry.... i should have clarified that - CTEK was not connected.
Car was parked, locked and not driven for all this time. AGM battery did not receive any charge. Weather is pretty warm these days too.....so no low temps.
When i unplugged the CTEK last week.... battery was around 12.6V give or take.
Today, it was at 12.25-30V
The discharge during those 5 day's is okay, battery is probably okay.
The SL55 has a fairly high standby consumption, so I recommend that you leave the CTEK connected, if you leave it for more than 2 day's.
Did you ever find out why the car is or was not charging the battery correct ?
You need to determine whether the battery is not holding a charge or whether there is an unusually large current drain while it's off. The ammeter in series with the battery that I discussed will tell you that.
If it's a large current drain, it could be a defective module of any sort not letting a CAN sleep. Or it could be a bad SAM. You would be advised to have a diagnostic scan, which will tell you. But first, you need to measure the current draw when the car has been off for 1/2 hour or so and all networks are supposed to be sleeping. If there's not a large current drain, the battery is not holding a charge. If you get it fully charged with the CTEK and it drops to 12.25 in a couple of days, I think you have eliminated charging circuit issues (since the CTEK is doing the charging) and reduced it to bad battery or constant current drain.
You need to determine whether the battery is not holding a charge or whether there is an unusually large current drain while it's off. The ammeter in series with the battery that I discussed will tell you that.
If it's a large current drain, it could be a defective module of any sort not letting a CAN sleep. Or it could be a bad SAM. You would be advised to have a diagnostic scan, which will tell you. But first, you need to measure the current draw when the car has been off for 1/2 hour or so and all networks are supposed to be sleeping. If there's not a large current drain, the battery is not holding a charge. If you get it fully charged with the CTEK and it drops to 12.25 in a couple of days, I think you have eliminated charging circuit issues (since the CTEK is doing the charging) and reduced it to bad battery or constant current drain.
On my SL55 the battery was discharging exactly the same way.
It could total discharge in 8-12 day's.
Those early models have a fairly high standby consumption, and that has been known for about 15 years.
On my SL55 the battery was discharging exactly the same way.
It could total discharge in 8-12 day's.
Those early models have a fairly high standby consumption, and that has been known for about 15 years.
Wow. That's pretty high. If that's the case, I'd advise OP to get in the habit of leaving the CTEK on pretty much always and see if that solves his warning problem.
Wow. That's pretty high. If that's the case, I'd advise OP to get in the habit of leaving the CTEK on pretty much always and see if that solves his warning problem.
Yep, i may have to get in the habit to plug the CTEK once a week.
The good news is....after 5-6 days with no driving and rear battery showing 12.3V .... when i started the car today, i did not get the red warning battery light.
It's still a mystery why a discharged rear battery will cause the red warning light on the dash.
It makes no sense....yet, it's a fact that when my red light was on, the rear battery was showing under 12 Volts with car not running. As soon as i ran the CTEK for 24 hrs, and the rear battery voltage went to 12.5V + .... the red light disappeared on its own and hasn't been back. Coincidence? I doubt it.
The other mystery of course is.... why the rear battery was under 12V to start with? At least once a week, I was driving the car to work and back (25miles trip, one way) .... why it did not charge to 12.x volts and stay there? How did it get to under 12V ? I see a healthy 14.3-14.6V at both batteries when the engine is running.
Yep, i may have to get in the habit to plug the CTEK once a week.
It's still a mystery why a discharged rear battery will cause the red warning light on the dash.
It makes no sense....yet, it's a fact that when my red light was on, the rear battery was showing under 12 Volts with car not running. As soon as i ran the CTEK for 24 hrs, and the rear battery voltage went to 12.5V + .... the red light disappeared on its own and hasn't been back. Coincidence? I doubt it.
The other mystery of course is.... why the rear battery was under 12V to start with? At least once a week, I was driving the car to work and back (25miles trip, one way) .... why it did not charge to 12.x volts and stay there? How did it get to under 12V ? I see a healthy 14.3-14.6V at both batteries when the engine is running.
I have the experience, that if a battery is fully or nearly full discharged, it is reluctant to accept current flow, due to some internal high resistance. It can take hours for a charger to fill in so much charge, that the battery "opens up" and accept full amp charging. I don't know why, or what it is called, but it is an observation. That might explain why you can't charge your battery, even on 25 mile trip, when it is discharged.
Still NO red warning light. Good.
Car has been sitting mostly in the garage but i had the CTEK plugged in on and off.
The weather cooled off (under 40F in the morning) and when i measured the voltage at the rear battery yesterday morning, with the car OFF and the CTEK disconnected for 2-3 days..... the voltmeter was seeing 11.8V. Clearly below 12 volts, again.
I decided to check the "stand by" consumption today.
I inserted my volt meter inline, let the car sit for 20-30 minutes so the trunk light went off and all accessories were off....and it measured 0.13 - 0.14 Amps.
It does not seem very high to me, given that these cars are known for their higher than normal parasitic draw. I would still like to hear your opinion on these numbers.
So, given the 11.8V at the AGM battery after 2-3 with no charge and the 0.13Amp draw when sitting - should i start shopping for a new AGM battery, next time i see the red battery light on the dashboard?
Or perhaps i can milk the current battery, using the CTEK more frequently and see how long it will last me before accessories start to shut off.
"This is an AGM battery, purchased from Auto Zone or one of the big chain parts stores. It was installed in March of 2017, so it's 2.5 yrs old."
I would find the receipt and take it back asap. It probably has a 5 year warranty so you might get a new one free or at a heavily discounted rate. Even if you can't find the receipt I would return it. Sometimes the stores keep records , bar codes etc.
It's difficult to diagnose electronics if your not starting off with proper voltage.
The 10.8 is the level that the car's electronic battery monitor will function at. A battery can't get this low unless it has a bad cell, a condition that the electronics are designed to detect.
Three days at .13A is 3*24*.13 or a little more than 9 Ah. The battery is a 70 Ah unit, so this would tell me it's not holding charge since 11.8 is the zero-charge voltage (see above link). If it were me, I'd replace the battery.
An AGM battery is totally discharged at 11.8 volts.
This is false. If there is voltage on a battery, then inherently there has to be a charge for a difference in electrical potential to exist. Further, if this were true, an R230 could not be started at voltages in the range of 10.8 to 11.8 volts, but of course we all know that is not the case.
Originally Posted by whoover
A battery can't get this low [10.8 volts] unless it has a bad cell...
This is simply untrue. For many years the voltage on my battery has regularly fallen below 10.8 volts, since I rarely drive it more than once a week. I can assure you the battery recovers and charges well above 12 volts, so there are no bad cells.
This is false. If there is voltage on a battery, then inherently there has to be a charge for a difference in electrical potential to exist. Further, if this were true, an R230 could not be started at voltages in the range of 10.8 to 11.8 volts, but of course we all know that is not the case.
This is simply untrue. For many years the voltage on my battery has regularly fallen below 10.8 volts, since I rarely drive it more than once a week. I can assure you the battery recovers and charges well above 12 volts, so there are no bad cells.
These voltages don't make sense. I assure you a battery at 10.8 volts will not start the car. Look at any voltage vs. charge table on the net. There are many of them and they're all consistent that 11.8 V is fully discharged.
I assure you a battery at 10.8 volts will not start the car.
To be clear, we are talking about the rear battery in the trunk. It doesn't have to turn the motor starter. It simply has to run the vehicle electronics and the starter solenoid.
The microcontrollers internal to each electronic module run on 5 volts or 3.3 volts. Automotive relays and solenoids are typically rated to operate with just 10 volts or sometimes even less. There is no reason for an R230's electrical system to quit operating at 10.8 volts.
To be clear, we are talking about the rear battery in the trunk. It doesn't have to turn the motor starter. It simply has to run the vehicle electronics and the starter solenoid.
The microcontrollers internal to each electronic module run on 5 volts or 3.3 volts. Automotive relays and solenoids are typically rated to operate with just 10 volts or sometimes even less. There is no reason for an R230's electrical system to quit operating at 10.8 volts.
Correct, the electronics can run at 10.8 volts. But a battery cannot drop below 11.8 volts unless it is defective. When you deplete the battery of all charge, it will read 11.8 volts, unless some consumer is connected when you are reading the voltage. In that case, the additional voltage drop could result in a lower reading. But a properly functioning (charged and/or charging) 12 volt circuit should never show a no-load voltage below 12.4 volts.
The rear battery is 70 Ah while the starter battery has half the capacity, 35 Ah. This is straight from the pdf that you posted. The systems battery does start the engine for eco start, if it has sufficient charge. It is also called to do a cold start if the starter battery has insufficient charge.
Assuming the current readings were taken correctly, this systems battery is fully discharged after providing around 10% the charge it's rated to store.
The systems battery does start the engine for eco start, if it has sufficient charge. It is also called to do a cold start if the starter battery has insufficient charge.
This too is wrong. On no account will the systems battery turn the motor starter. Whatever "eco" start may be, it is not defined by Mercedes for an R230.
Originally Posted by whoover
But a battery cannot drop below 11.8 volts unless it is defective.
Yet my systems battery has been doing this practically every week since 2007 without damage. How can that be? Let's look at it from a technical perspective.
If I connect a 1-ohm resistor across a battery with 11.8 volts, 11.8 amps of current will flow. If I leave the resistor in place long enough, I think you will agree the battery voltage will fall to 11.7 volts without damaging a cell in the battery. At some point it will have fallen to 11 volts -- still undamaged -- and this happens to be the voltage that the Mercedes WIS gives as being the lower limit for an adequately-charged battery.
Last edited by bobterry99; 10-31-2019 at 06:27 PM.
SInce you refuse to accept any of them, we're going to have to agree to disagree. BTW, if you place a 1 ohm load on a dead battery at 11.8 volts, very little current will flow. And no, Ohm's law has not been violated. You have failed to account for the very high internal resistance of the dead battery.
SInce you refuse to accept any of them [battery tables]...
With respect to those tables a battery is regarded as completely "discharged" if it can not start the engine. Those tables might apply to some vehicles with one battery, but they are not applicable to the R230 with its two batteries.
Originally Posted by whoover
You have failed to account for the very high internal resistance of the dead battery.
No, because a battery with 11.8 volts is not "dead", and it's internal resistance is negligible. And as seen below, a battery with 10.9 volts can power the vehicle electrical system.
If you look at the attached screenshot from the "Dual Battery On-Board Electrical System" document conditions for the system to operate normally are that both batteries are greater than 10.8 volts. Obviously if a battery with 11 volts implied a defective battery, the system would not be described as operating normally; also, surely a fault would be set and a message indicating "defective battery" would show in the cluster. But neither the message nor the fault even exist, since there is nothing abnormal about the systems battery falling well below 11 volts.
Last edited by bobterry99; 10-31-2019 at 11:07 PM.
...conditions for the system to operate normally are that both batteries are greater than 10.8 volts.
While looking into a starting issue for a 1999 SL I came across the following statement in the Mercedes WIS: .
[The opening time of the fuel injectors] is dependent upon the battery voltage. The ME control unit extends the injection time in order to compensate the quantity injected if, for example, the battery voltage is low. No further engine start is possible below a voltage of approximately 7 volts.
From experience I'm fairly certain my 2000 S500 would start with a voltage of 11.3 volts. I'm unsure about 11 volts, but I'd risk my life betting that it won't start with 9 volts. I'm incredulous that Mercedes suggest 7.5 volts is adequate.
10-15-2019, 03:32 PM
