This is just something I'd like to share with other E46 owners. It may not be true but might help in some ways.
My car is a 2003 E46Ci and I bought it in 2006. The battery is an original low maintenance one. I've been told that it's a manufacture battery, which originally comes with the car.
Recently, I had some problems starting the car but it was due to my long absence from starting and driving it. Anyway, the point I'm trying to make here is that another sign to show that it's time to change the battery is the coloured monitor / screen. I've just noticed that the colour will change to some abnormal colours when I didn't start the car for the last 2 days, prior to today.
I'm not entirely certain that this is a sign but it could possibly be an indication of a weak battery, although the sign on the battery itself is positive. The colour changed back to normal when I've driven it around for approximately 1 hour. Could anyone confirm this?