This is the right answer.....

 

It’s that damn smart alternators that modern mercs have. They only start charging the battery when they really have which in turn shorten battery life. But hey. It saves a few polar bears apparently.

 

....

 

OK, thanks for all the advice.

Coming back to this thread because I was driving about 30 minutes yesterday but still could not put the car in standby. We WERE using the seat heaters and it has been pretty cold here 20-30F. I have put the car in standby a few times since my original post. Maybe the trick is driving about 45 minutes at a time, since I no longer drive it daily. But I get the point of the trickle charger, to keep the battery charged all the time.

I'm thinking to replace the battery AND get the MB trickle charger. I need to double check my service notes to make sure I haven't replaced it yet. It tested OK at my regular service in 06/2025. Would my local parts department give the same price for the charger as online?

 

@SemperFi I'm heading out tomorrow to my local dealer to pick up one of these trickle chargers. How long would you say the cord is? My outlet is back by the garage door, so about a car length. Is it safe to use an extension cord? And is this something I leave plugged in all the time, or do I need to unplug occasionally?

Will I leave the hood open with this connected, or will the hood be closed? I don't want to pinch any wires, obviously.

Thank you.

 

You can try to PM @SemperFi for a response, but he's on a self-imposed "hiatus" of an undetermined time from the forum.

 

OK didn't know that. Maybe someone else will know. The cord in the image looks pretty long. I can always try the extension cord I have.

 

I have one of those with the wires permanently connected to my aux battery in the trunk. With the disconnect plug in the trunk it has more than enough cord length to reach the car from the garage wall socket. Good luck.

 

So I want to charge the battery in the trunk (where) not the battery in the engine compartment? I did read my owner’s manual, but it’s not helping. Do you leave the trunk open when charging?

Thanks. I’ll try googling.

 

The starter battery and auxiliary battery are located in the trunk (starter behind d/s rear seat in trunk, aux battery at the p/s behind carpeted covers where the fuel fill region is.

The engine compartment, you’ll have your positive terminal with the red sliding tab, and a ground post about 10-12 inches away in the direction of front bumper. You could remove the plastic covers, bolt a quick connect pos/neg and route it to the wiper cowling. This way you’ll never need to open hood/trunk and the connection is hidden from view.

 

I can close the trunk with the small red & black wires passing under the seal.
Having said that, I caution to be careful not to drive away with the trunk closed and the wires still connected - don't ask me how I know this...

 

Today, I drove one hour each way. Turning off the car in between. Total of two hours today. No use of electrical except radio. When I got home I still couldn’t put the car in standby. Is this a sign that one or both batteries need to be replaced? Car is a 2020, so six years old now. I have a service appointment in one week.

 

It is and has been telling you that a battery or two are junk.

 

Because I’m not driving it daily? Or because it’s 6 years old? I’ll double check my service records to see if I ever changed the batteries. I don’t think so.

 

Batteries fail. See it every day.

 

I replaced the starter battery (12V?), in 11/2022. Seems reasonable to change it now.

 

The system battery seems more likely.

 

System? Do you mean the 48V auxiliary battery? Maybe I have them confused. The alarm in the instrument cluster was for the 12V battery. I’ll find out in a week.

 

Sorry, I was thinking about my 2016. Your car apparently has different batteries. Good luck!

 

So I now have the trickle charger installed in my S560, in the trunk. There is an ominous warning in the small manual about HYDROGEN GAS. And don't cover up the charger while charging. My car is in the garage with the electrical outlet where the trunk is, near the garage door. I have a gas water heater near the hood. How best to make sure any hydrogen gas (if any) is vented when charging? I was going to keep the trunk closed, but is that a bad idea? We store a can of gasoline in the garage for weed trimmers and such. Will it be OK if I keep it away from the charger?

They hid the wiring behind the panels. I didn't realize there is an option to connect to a 12V source. That would be useful because I just bought a 40 lb backup battery for our laptops and phones that I could use to charge in an emergency. Is it obvious how to remove the trunk panels if I want to access the connection point?

 

I always charge my 560 using the connectors in the engine compartment, hood open no gas problem.

 

Thanks. But is it near a gas can or a gas water heater? Do you have any ventilation? Those manuals can be over cautious.

 

A battery getting over-charged will produce Hydrogen if failing memory serves. Stinks. That certainly was an issue with lead/acid batteries. Don't know that it is an issue with Glass mat batteries.

 

CTEK support told me that they have no extension cables that fit this Mercedes (CTEK made) charger. I was going to put the control box outside the trunk, as some reports say it gets pretty warm and/or hot when charging? Which appears to take around 4 hours maximum? This doesn't seem right since MB gave me the 12V input, so it must be in two pieces. I haven't had time to look at it yet but was going to take a peek at the wiring this weekend.

 

It's been years since I do this on all of my cars , some of them only when I'm traveling for weeks, some of then that we don't drive them during the winter time, never had any kind of smell, my garage is climate controlled....