I had the opportunity to observe more how CTEK works. Once the battery is fully charged, it will stay at a minimum voltage of 12.63 V for a few days.
After a few days, and I don't know how many days, CTEK will "play" charging the battery between 12.63 to 13.18 V. I forgot to measure the time interval.
Once I left the car for about two months and when I started it, it was the first time for me to hear it cranking forever. It was when I didn't use CTEK. It must be noted that I am using a "cheat version" of battery. This is an ordinary battery by Motolite, given free by my friend. I never experienced this with the stock battery, not until it died.
Right after turning on CTEK, voltage will climb slowly, for about a minute, up to 14.05 V.
This is a little lower than the charge coming from the alternator at 14.46 V.
I do not know what is my stock battery, if it's an EFB or AGM. All I know is the brand, Yuasa. It is unfortunate that I wasn't able to observe CTEK on my stock battery, the way I was able to observe it now.