I had similar issues with my Sebang battery earlier in the year, not using the car much I charged it during the week, but it didn't make much difference.
Once a battery is on the way out, if you are not using the car to charge, it is literally game over.
I replaced it with a Yuasa 9000 AGM and it has been fine ever since.
Coding is easy with Vagcom / Obd11, you just need to put a different code in to tell the car it is a new battery and if you have changed type to AGM.
For a code, I put in the date of battery replacement, it accepted immediately.
Coming up to "Black Friday, I am sure there will be a few deals around on car parts.