It's the CTEK 56-380
CTEK (56-380) Comfort Indicator Panel M8 for Top Post Batteries
https://www.amazon.com/dp/B002OHXX60..._8lZBFbYNY6PPZ
I also have the extension cable which is thin enough to fit between the closed trunk.
Or if I'm quick enough I can prevent the lid from closing completely.
The car is in my own garage so I don't care too much if the trunk is fully closed or not.