You can get a bosch one that says "S3" on it (S4/S5 available too) which is sorta cool
One of my A4's has an Exide battery, the other a halfords one. Both seem fine, but the pervious owner that bought the Halfords one baught the wrong one, as its tiny and just about fit to start a 1200 corsa. Struggles a bit in winter, but its still working fine 2 years later.
If the battery in currently is a 50ah and the bosch S5 is 63ah would there be a noticable difference? I tend to leave music on all of the time and seem to be running it flat all the time. Would it also benifit if I got a leisure battery such as this to stop me draining the battery so often?: Bosch Leisure Battery Type 677 - 75ah