Some follow-up on Halfords failing to code my new battery fitted by them.
Everything was working OK, but I was worried about the longevity of the battery and was going to find someone local with a VCDS as suggested by this forum.
However, I have a Vgate adapter with WiFi connection anyway and started looking at the diagnostics with different softwares on my Android phone. To my surprise the CarScanner App actually has the ability to do quite a lot of coding built into it for certain models (incl. most Skodas) - google car scanner to get to their site and look at the tab for "coding and service" It shows which cars it will code.
Note that to see the coding button on the app you need to have setup a connection profile for your Skoda first in settings (for my Octavia 3 1.2 TSI it is the second profile on the Skoda list) and it has to be connected to the car CPU by WiFi or Bluetooth, whichever you have on your adapter.
When you start, it strongly recommends that you backup all your car settings before changing anything and warns that it takes some time (about 5-10 minutes) Then I scrolled to the battery section and it has the standard 4 parameters: Capacity, Type, Manufacturer and Serial number. I changed all of them as suggested in this forum. Capacity from 59 Ah to 70 Ah, Type from EFB to Fleece (for AGM) manufacturer from JCB to HAL and changed the serial number from 11111111111 to 11111111112. It happily accepted all of these parameters and showed them as the stored parameters when I looked later.
A word of warning - the free version of CarScanner only lets you change 3 parameters so I had to buy the pro version for £4 halfway through programming, but if you don't want to buy it, then don't change the manufacturer code as that is the only one which doesn't actually need changing and just change the serial number to make it realise that you have a new battery plus the capacity and type if you need to.
Everything still works OK and hopefully it will be charging correctly now, but I am not going to play around with any of the other myriad of settings it will let me code.
There you are - Battery coding for a few pounds.