Hey
How old is the battery? Expectations for modern batteries are about 3-5.
Is the car in regular use or is it left to sit for extended periods? If it's left, do you leave the CTEK connected? Have you metered the battery to know what voltage you're getting?
You don't say what model of CTEK you use but you'll need to run in
Recond or
Supply mode and depending on the model you have, it may not support this functionality.
Not sure if the battery is deeply discharged but you'll need to use a multimeter before you start because there is a threshold of about 6-8v, below which a CTEK won't recognise it. You can connect everything up and not get any indication of what's going on, only that it hasn't worked when you meter it or try and turn the car over.
I bought a
Ring 612 smart diagnostic charger a few years back as the interface was useful for monitoring progress. You can find them for about £30-40 than the MSRP on the link and it has worked pretty well in your scenario.
I gave up on CTEK (I had them as OEM rebranded via Porsche) and moved to NOCO, more versatile and I carry a Noco Boost (sufficient to jump start 12v) + the connectors and build is more robust.
Hope this helps.
A