how do u remove backseat to get at the battery
http://www.bimmerfest.com/forums/showthread.php?t=263471. It's called brimmerfest. Look thru this website. Your answer is there.
I don't have much experience with such Old BMW's, but the Battery should be in the Trunk, not under the Back Seat..
You have to lift rly hard on the front of the back seat, there are two latches located roughly around the middle of each seat. It will feel like your going to break something but you won't. You'll also find the alarm system module back there, if you have it. If you only need to get to the battery for a jump, there is a positive terminal in the engine compartment as well, passenger side back
What Greg said, just pull up hard on the front of the back seat butt cushions.
Looking for a Used 5 Series in your area?
CarGurus has 20,408 nationwide 5 Series listings starting at $1,950.
Search BMW 5 Series Questions
BMW 5 Series Experts