I am sure this must have been covered somewhere, but I am unable to find what I am looking for through a site search or in the manual (which is frustrating).

2018 e63 AMG. This car doesn’t get driven much so I’d like to put my CTEK on it. The battery was replaced by the dealer a few months ago when I bought the car used with 11k miles. I’m not having any problems, but would like to keep it that way. Dealer confirmed it’s an AGM battery. When I connect the charger to the positive blade and the negative stud under the hood, it only charges to 50%. I am new to MB but I know Porsches have a lockout mode for charging unless you do a certain door close/lock sequence. Is that what’s happening here? Recommendations appreciated. Thanks!

What do you mean it charges to 50%?

If it’s a new battery and your first time hooked up, it could take well over 18 hrs to get it fully charged up

Or even more time, depending on the charger current rating: 4A ctek will take almost twice as long as 7A charger…

Luckily, there is a simple solution that does not require battery charger - Standby mode.

My E63 claims it will be able to start the engine after 33 weeks, if put into Standby with fully charged battery.
Caveat is remote services (me connect) and alarm are turned off when in standby mode…

was just getting a message in my '19 about low battery, needing to drive car. So I hooked up the charger and left it connected overnight and the battery is back up to 100%. It did take quite a while to even make a small dent so make sure it stays connected to charger sufficiently long

I would also recommend you install the dongle CTEK provides so you only have the connector peeking out from the battery compartment. I've found you can run the cable straight to the front, bring the hood down and even a custom California Covers cover will fit. Looks very slick when you open the hood.

I also learned (every vehicle has its own charger, but I missed this best practice) that one should recondition a battery at least once a year. So I added a note to my iPhone with all the vehicles and when I reconditioned.

Look up your battery online and confirm it truly is AGM. 2018 OEM/replacement battery is not AGM. If it is AGM, make sure the mode on the charger is AGM, (I've standardized on the MXS 5.0, which has a mode button labeled AGM). I'm not sure what the car could do to stop a charger from completing its full cycle assuming you connected the CTEK dongle directly to the battery terminals (not some spot out under the hood somewhere).

Thanks everyone. Turns out I just had not charged long enough. So for the record, you can trickle charge from the pos blade and neg stud under the hood. Charged to 100% overnight.

Yeah

on subsequent charge up, it may take less than 12 hrs (if you do this once a month or two)

Installing the charger dongle is highly recommended, as it's polarized and ensures your charger will always be connected correctly. Connecting a charger backwards using the cable clamps when you experience a momentary attention lapse creates huge problems.

I'll also chime in and say that you don't need an expensive trickle charger. I have a basic battery tender from amazon and it works just fine and has caused no issues.