Flat battery

[_deano]

This morning i had to jump start the car as my battery was flat (again!). The first time it went flat was about 2 weeks ago after the car had been left on the drive for 2 days. This time my car was left on the drive for only a day and it didn't want to know. I'm thinking that the battery could be the original and so it could be time to change it. How long do car batteries last before changing it (bearing in mind that the car is just over 5 years old)?
Also, what would be the best place to buy a car battery for a BMW 530sport?
And where can i dump my old car battery?

thanks

DJ