Originally Posted by EricP3
I do not know if it is the original or if the previous owner had it replaced.
Warning: speculation ahead!
If the battery is labelled like other batteries I've put in on non-BMW's, there may be some label or indicator of month/year when the battery was manufactured.
While this doesn't tell you how long it's been in the car, clearly if a battery was made in 2010 it's not the original battery in a 2008 model year car.