Good to meet you on Saturday Paul A6
Sometimes it's hard to find a true ignition fed power source in the fusebox as is the case on my Honda CR-V...could not find a single feed in there...ended up with a permanent feed and selected then dash cam (Nextbase 512GW) to power down after a few minutes. The good thing about this is it will not drain the battery and also it comes alive if the car is knocked so good for added security.
As with the replacement battery, 'you get what you pay for' and quality is not cheap but I know @Magnet will back me up on this one.....get a branded make and albeit you pay for it, you won't regret it. If you are in Bournemouth area at any time, there is a superb Battery wholesaler, Bournemouth Battery Centre who can supply a branded one at a very reasonable cost (even cheaper if I give you my trade account name, let me know if you need it).
Also, niedzial1983 is correct as it will need coding in for the vehicle to recognise the new battery charge status, otherwise it will always work off the old battery condition and not charge properly. It's a quick procedure that can be done by anyone with a VagCom.
Let us know how you get on with it all
Cheers, Trevor