I leave my CTEK on all the time but I think once it detects a full battery it just tickles rather than ramps up.....Have you tried powering up the charger once the bike has powered up and stabilised? This should force the charger into full charge mode. This works on my Noco 2 charger, but the voltage is only maintained at around 12.2 volts, as it has a maximum output of 2 amps. My basic 5 amp Halfords charger shows just over 5 amps charge when connected to the slave battery, but I wouldn’t trust it directly onto the bike battery.
You also need decent jump leads and clips. I have some I made from scratch a few years ago, which have a good surface contact area on the croc clips. It also helps if you connect the slave battery a few minutes before powering the bike up. This allows the two to stabilise.
I'll try on the slave battery I think as that does struggle
But I think Wessie hit the nail on the head and I need a car battery