So over the coldest winter my A4 was being a little sluggish turning over. It never failed to start but always laboured a bit.
Every now and again from cold I would start it up and 'Brakes' would appear on the DIS accompanied by a beep and the handbrake indication light flashing. Brake pads will need replacing in ~6-10 months or so and fluid is at a happy level in the reservoir.
Some googling revealed it could have been a dying battery, which is supported by the fact it was labouring to start. So I stuck a new Bosch S4 battery in and it starts on the first crank from the starter but twice now since changing the battery I've had the flashing light, 'Brakes' on DIS and the beep. As I said brake pads aren't dead yet and there is plenty of fluid in it.