rmorin49

I am using a CTEK on my SL when it isn't used on a regular basis. My garage is not heated so it does get well below freezing during the winter months when I am not driving the SL at least once a month.

​​​​What is the correct mode to use for maintaining the batteries in the SL? I think I remember reading that the "snowflake" mode should be used. Is this correct? I thought it was the mode used in cold environments and also for AGM batteries.

Isn't the main battery a traditional lead acid battery? What about the small auxiliary battery? I replaced my auxiliary battery last year and it also looked like a lead acid battery.

hornethandler

The “snowflake” mode provides higher charging current for cold weather applications.
The main and small (eco start/stop battery) are AGM lead acid batteries.
Here’s the part numbers for a 2019 SL450:
Eco start/stop battery: A211-541-00-01; and
Main battery: A 001 982 82 08 26.

JettaRed

iTrader: (1)

I don't think it has gotten below freezing in our area this year. I know I have water in containers in the garage and they haven't frozen. That aside, I don't think there is any harm leaving the CTEK connected to the main battery if you are not driving your car often. I drive mine daily, so I don't have this concern. Now, my 2004 SL500 is another story. I used to connected that whenever I wasn't using the car. But, it stayed outside.

Bitbytr

Slightly off topic but the discussion of batteries (and their part numbers: thank you!) raises a query I've been mulling for a while. After I start off and drive a while I might come to a stop at a light: the 'ECO' display is yellow but often will then change to green and the engine will appropriately cut out. In other words, the 'ECO' display doesn't often actually show in green even after a good (say) 20 mile cruise with the only 'consumable' being the head unit. I am wondering if that's indicative of the battery losing its health meaning a replacement will soon be required?

And, if so, which battery - the one in the trunk or the one in the cabin? 🤔

Edit: I found a really informative thread here (https://mbworld.org/forums/sl-class-...ry-type-2.html) and am now assured its the ECO start battery that's going south. I'll have them both checked. Thanks to all who contributed to that thread a couple of years back ...

rmorin49

Jetta, you must have taken a long winter's nap. We had a very cold spell earlier this year when the temps were in the single digits for a couple nights at least in Hagerstown.

Is the "snowflake" mode the correct one to use since the batteries are AGM even if ambient temperatures are well above freezing?

hornethandler

According to CTEK’s manual, (see link) use the cold weather option for charging at low temps.
The normal and the cold weather modes are suitable for AGM charging.
https://cdn.shopify.com/s/files/1/01...07522301633849

JettaRed

iTrader: (1)

I guess it's just warmer in Middletown. And, the "snowflake" mode is for liberals in California.

rmorin49

I'll need to change that to a different icon on my CTEKs. I'm far from a CA snowflake.

JettaRed

iTrader: (1)

Glad to hear it!

rorywquin

My CTEK instructions say to use “Snowflake” for AGM batteries. They also confirmed this by email.

rorywquin

Snowflake mode is correct. It is also used on other LA (Non AGM) batteries when temps are very low.