A few weeks back the battery packed up on the (missuses) Touran, it was the original factory fit battery (now nigh on 10 years old) and had been sluggish on startup for some time. I figured it was on it's way out, you'd turn the key and there would be a pause before the engine lurched into life (the dying battery obviously couldn't crank the engine fast enough to get a smooth start so it lurched into life which wasn't ideal). Anyway, it finally gave up the ghost and wouldn't crank, typically on a Friday which would make it harder to sort a replacement over the weekend for Monday's school run.
The O.E battery was made by Varta and carried the VW ref of 1J0 915 105 AD:

I am happy to give
Tayna batteries a solid recommendation for replacement batteries based off of their price and service, they sell Varta batteries and being the original battery was made by Varta I was more than happy to fit another one of theirs. Handily Tayna had a cross reference for the VW reference to the equivalent replacement Varta battery which had the correct dimensions, output and terminal layout, and for £65
including Saturday AM delivery I was pretty impressed, it turned up by 9.30 AM on the Saturday and by lunchtime the car was back on the road with a much more positive start!
Link to the specific replacement battery I purchased
here (it was a Silver dynamic spec battery as well which as I understand it is Varta's top spec replacement).