Here's an update for everyone:
Firstly thank you everyone for your help and insight, with that being said, I was able to replace and code the battery on my own. 😁 The only real thing that I think can hold anyone back from doing this is either a lack of an OBDII scanner with coding abilities, a wrench with an extension or two and determination.
A local garage quoted me at £20 to fit a battery but when I asked if this included coding they said no. The other was a Varta specialist going for around £40 up to £80 just to fit one in. Halfords had their own brand EFB battery at £186.99 plus £27.99 fitting. 🤯
So with that being said let's go over it.
I have a 2017 Skoda Superb MkIII fitted with an OEM Banner EFB 6R0 915 105 B 12V 69Ah 360A DIN battery. The main key points are the battery type, EFB, the capacity 69Ah and the dimensions, length: 275 mm, width: 175 mm and height: 190 mm.
I realised my battery was dying/dead when I had the error message "Manoveure braking unavailable" pop up time over time and then one day it wouldn't crank without the help of a jump starter. It wouldn't even hold any charge even when charged with a trickle charger. 6 years, low miles over Covid (still low miles now) and plenty of cold winter starts probably killed the battery.
I ordered the ever popular Varta AGM E39 12V 70Ah 760A 570 901 076 D86 2 battery for £145 including next day delivery. One reason I picked Varta is because it's also an OEM choice battery found in some other VAG vehicles. The key differences are that it is an AGM type battery, the capcity is 70Ah and that it is slightly longer at 278mm but the same width: 175mm and height: 190mm. The extra 3mm is nothing to be concerned about. It arrived next day from Tayna and was pretty much fully charged when I tested it with my trickle charger.
From what I understand an AGM type battery should last three times as long as a regular battery, compared to an EFB type when compared to a regular battery which only lasts twice as long. The only issue is that AGM batteries don't like heat - hence why there is a thermal battery sleeve in the Superb.
The other thing that needs doing is that changing from an EFB to an AGM type battery needs coding. I originally got the OBDeleven when it was on sale with a voucher, however at the time you could get free credits (not anymore) but in order to do any coding or adaptations you'll need a Pro subcription. So you're looking at just under £100 together in order to do it (the OBD2 device is £60 and the 1 year Pro plan is £50 separately). This together can really put someone off, nearly did for me, but it can save some money clearing codes, diagnosing faults on the car, service intervals, and in my case when I managed in a very roundabout way of getting Pro, save money.
That and you need a 10mm and a 13mm sockets with a wrench and extension bar.
As @BillyParkersays, it took longer to get the battery swapped over than coding it in.
You first disconnect the negative terminal first by loosening the 10mm socket, then loosen the postive terminal and move them aside - it can take a lot of loosening and nudging to remove the terminals from the battery. I wasn't keen on the idea of using a screw driver to wedge loose the terminals so that's probably where I took the longest.
At the front of the battery there is a bracket with a 13mm bolt that you can undo with the extension bar (in my case I used two) and the removed the bracket which can be finnicky. But once that is out, you'll need to pull the battery towards you so it leaves the battery tray mounts at the rear, then you can remove the thermal battery sleeve, and then carefully lift the whole battery out - it was pretty heavy especially when you're leaning forwards and you have to be cafeul that you don't want to drop it on the car panels.
I used the plastic cover from the positive end of the new battery to cover the old one - there is also a plastic nub that I used to seal up the old battery to stop any leaking.
Give it a clean at the bottom of the battery tray - there are several mounting holes you can use but I can't imagine anyone using a smaller battery. then lift and insert the new one into the bottom battery mounts and push until it's fully in. Here I put the thermal sleeve on but I imagine it might've been easier to put the sleeve on first then push it into position.
When you're connecting the new battery, do it in reverse, connect the positive terminal and then the negative. I got a few sparks when trying to seat the negative terminal but once it's in there wasn't anything to be afraid of.
Then you can add the battery bracket and hand tighten them all. That's the hard part done.
The next part was coding, I turned the ignotion on and instantly nearly every warning light came on - low tyre pressure light, brake disc fault, hill hold disabled, start stop disabled, cruise control disabled, auto parking brake error, steering angle error, digital radio antenna fault, emergency SOS fault and so on. Kinda scary.
I connected my OBDeleven to the car and went straight to code the new battery in, tapping onto Control Unit, Gateway 19, Adaptation, then Battery Adaptation, where you are presented with your old battery settings. Incidentally a lot of it wasn't accurate, I had a Banner battery which was labelled as JCB instead of BA2 and the Battery serial number was just 1111111111. The only correct things were the Rated battery capacity at 69 Ah and the Battery technology EFB.
So this is where you need the Pro version of OBDeleven, which has a green checkmark on the bottom right which you hold to save your new values, otherwise you're faced with a red padlock and needing to splash out £50 or so. Thankfully I was about to get around this and save myself a bunch.
So the new settings I added were 70Ah, changed the last digit on the Battery serial number to 1111111110 (10 digits, doesn't really matter what), changed the Battery manufacturer to Varta's code VA0 (or VAO, it apparently doesn't matter which one as long as it doesn't flag up an error) and the new Battery technology Fleece. Tap and hold the green button (at this point I should at looked for a test on the app but didn't) and then turned on the engine.
I did a full lock left to right (which instantly cleared one or two faults) and then did a little drive. The engine turned over instantly and the steering and acceleration felt a lot more tighter. When I next stopped I turned the engine off, key out of the ignition, then open and shut door, key back in and only turn on the ignition - I cleared all the remaning faults and then it was all good. I even silenced the Superb's remote liftback beeps while I was at it.
So thanks everyone, and if anyone is interested in doing it themselves I hope this helps, given this new experience. 😁