R230 trickle charging issue

Page may contain affiliate links. Please see terms for details.

PPC

New Member
Joined
Nov 30, 2022
Messages
9
Location
Somerset
Car
Current Toys: S63 Coupe, R230 SL350, (Sadly gone: R129 SL320, R231 SL350, ML350)
So I have a 2007 Sl350 that was picked up as a stop gap car. it not used much like many SL's. I used to use a Noco Genus 10 charger to keep the front battery up to charge and that worked fine. However, I had to sort out a little bit of rust in the boot so pulled out the Aux battery and did that work. Once I popped everything back in I put some charger terminals onto the aux battery and started to see a very odd behaviour.

The car trickle charges for a few days but then either records a battery short or just seems to run the battery flat. The remote goes dead so I have to open the car with the key manually. Then I start the car and everything seems to spring to life. The battery charger then seems to say : Oh hang on! no I am not completely flat I am actually green! look see? and then starts behaving normally until it repeats the saga all over again.

If I run the car it starts with the usual AUX battery is dead error but once I have run 20 miles or more and give it a good cycle all the batteries read 12v+ and everything goes back to ok.

Has anyone seen anything similar? I should say that I have an S Coupe that I share the charger with and it works perfectly ok on that.
 
So I have a 2007 Sl350 that was picked up as a stop gap car. it not used much like many SL's. I used to use a Noco Genus 10 charger to keep the front battery up to charge and that worked fine. However, I had to sort out a little bit of rust in the boot so pulled out the Aux battery and did that work. Once I popped everything back in I put some charger terminals onto the aux battery and started to see a very odd behaviour.

The car trickle charges for a few days but then either records a battery short or just seems to run the battery flat. The remote goes dead so I have to open the car with the key manually. Then I start the car and everything seems to spring to life. The battery charger then seems to say : Oh hang on! no I am not completely flat I am actually green! look see? and then starts behaving normally until it repeats the saga all over again.

If I run the car it starts with the usual AUX battery is dead error but once I have run 20 miles or more and give it a good cycle all the batteries read 12v+ and everything goes back to ok.

Has anyone seen anything similar? I should say that I have an S Coupe that I share the charger with and it works perfectly ok on that.

My guess is your battery is goosed.
 
So I have a 2007 Sl350 that was picked up as a stop gap car. it not used much like many SL's. I used to use a Noco Genus 10 charger to keep the front battery up to charge and that worked fine. However, I had to sort out a little bit of rust in the boot so pulled out the Aux battery and did that work. Once I popped everything back in I put some charger terminals onto the aux battery and started to see a very odd behaviour.

The car trickle charges for a few days but then either records a battery short or just seems to run the battery flat. The remote goes dead so I have to open the car with the key manually. Then I start the car and everything seems to spring to life. The battery charger then seems to say : Oh hang on! no I am not completely flat I am actually green! look see? and then starts behaving normally until it repeats the saga all over again.

If I run the car it starts with the usual AUX battery is dead error but once I have run 20 miles or more and give it a good cycle all the batteries read 12v+ and everything goes back to ok.

Has anyone seen anything similar? I should say that I have an S Coupe that I share the charger with and it works perfectly ok on that.
Completely normal.

Much discussed on here. There’s a gentle phantom drain, so if you don’t use an R230 for a month, the Auxiliary battery will go flat “first” to protect the starter battery. Drive the car for ten miles or so and the Aux battery will come back on line so that you can power the hood, air con etc.

First step is to fully recondition AND charge your Aux battery to see if the battery can be fully charged again. If it’s too bad, it may need a new Aux battery

But, if like most SL owners, you’re leaving the SL unimused for more than a month, you will need to regularly charge or trickle your auxilliary battery
 
Thanks all. I am going to try pulling the battery out and charging it while it is off the car. If it holds the charge and gets to maintenance mode then I know the car is waking up and being leaky
 
I have a trikle charger on both batteries never had an issue
 
I used to just charge the front battery and all seemed to be OK then moved to charging the back on instead and it seemed to work until I took the battery out to sort out some light rust. I stuck the Aux battery on repair over night and am now charging it up from empty so I guess we will know if its new battery time soon then I can do the same to the front one.
 
My understanding is that the "correct" routine is to charge the Auxiliary battery (in the boot), as it's designed to top up the starter battery, as needed, while driving if the alternator hasn't done enough work to replenish the energy used by the start..

It's the Aux / Consumer battery that gets all the load from the roof, HVAC and day to day nonsense.

It makes sense that MB would have designed the system so that only one battery needs to be charged from an external source, that being the bigger Consumer battery.

Are you taking the battery out because you can't run a cable to it ? In general removing the battery always runs risks of resets for the ever more complicated circuitry. With later cars, and possibly this, the car's system needs to "know" how much juice is in the battery for it to charge correctly, so there's a whole range of ...nonsense... that means that certainly newer cars allegedly need to be fitted to their new battery.

(There are greater electrical experts around who are welcome to weigh in with the exact reasons which are generally beyond my pay grade."

If you can, in general, it's better to cable the battery charger / conditioner to the car, than to remove the battery.
 
Be aware that one should remove the rear battery neg connection before removing the front starter battery. This from MB training manual..
1712747808802.png
 
Regarding external charging ..
1712748173978.png
 
My understanding is that the "correct" routine is to charge the Auxiliary battery (in the boot), as it's designed to top up the starter battery, as needed, while driving if the alternator hasn't done enough work to replenish the energy used by the start..

It's the Aux / Consumer battery that gets all the load from the roof, HVAC and day to day nonsense.

It makes sense that MB would have designed the system so that only one battery needs to be charged from an external source, that being the bigger Consumer battery.

Are you taking the battery out because you can't run a cable to it ? In general removing the battery always runs risks of resets for the ever more complicated circuitry. With later cars, and possibly this, the car's system needs to "know" how much juice is in the battery for it to charge correctly, so there's a whole range of ...nonsense... that means that certainly newer cars allegedly need to be fitted to their new battery.

(There are greater electrical experts around who are welcome to weigh in with the exact reasons which are generally beyond my pay grade."

If you can, in general, it's better to cable the battery charger / conditioner to the car, than to remove the battery.
I have removed the batteries because I wanted to see them both prove to me that they are capable of holding a complete charge and that they are not as OneForTheRoad suggested done for.
So, overnight, I ran a reconditioning cycle on the aux battery and set a normal charge cycle on it this morning and that is now sat completely charged with the Noco auto Switched to state monitoring.
I have swapped the charger over to the starter battery and that topped up to full almost immediately and that too switched the charger to monitor status.

So I know the batteries are at least in an ok state. I will leave them out for the rest of the week just to prove to myself that they are really ok.

What you are saying about the car needing to know its battery sounds plausible. I have the 3.5 V6 and seem to remember the chap on YouTube from ThreePeaks saying something about the battery needing coding to the car. This is most likely entirely self caused like most things with these cars.

Everything was fine. I was crock clips to charge the front battery while the car was off the road. Then having watched some guides moved to clip charging the rear battery. All seemed well. Then I took the aux battery out for a few weeks and sorted out my rust spots. When I put it back, I put a permanent connector onto the aux battery but when it started charging it would get to the full status then suddenly drop to empty and stay there until I started the car. Then it was almost as if the car starting would let the battery come back to life and it would charge without error until the next time I looked and the battery would be dead again.

The car came without its manuals or second key so it's a bit of a hit and miss relationship because I am guessing how it works.
 
If its the original battery then its time for a new one.
I might have an internal fault that makes contact, but when put under load breaks contact.
If it looks like this its the same as mine, but mine hasn't worked for years and as far as I am aware its only function is for stop/start, nothing else is effected.
s-l225.jpg
 
If its the original battery then its time for a new one.
I might have an internal fault that makes contact, but when put under load breaks contact.
If it looks like this its the same as mine, but mine hasn't worked for years and as far as I am aware its only function is for stop/start, nothing else is effected.
View attachment 155515
That looks like the aux battery off the R231 whereas the op has the R230 with a full size aux (consumer) battery?
 
That looks like the aux battery off the R231 whereas the op has the R230 with a full size aux (consumer) battery?
Yes my battery is the big one. The good news is its behaved itself over night and is still sat in monitoring mode.
 

Users who are viewing this thread

Back
Top Bottom