I very recentlyl bought a 2000 540i (the car was placed in service in 10/99). It appears to have the orginal battery, making it almost four years old. There appears to be a coding to it. If a green dot appears in a window it is fine. A black dot means charge. A yellow dot means replace. Assumnig I am looking at the right thing, the window has a black dot. I gather BMW puts the battery in the back to keep it away from engine heat and give it longer life. Should I replace the battery? What kind of life do people generally get from their batteries? Thanks.