To replace a BMW battery, remove the negative and positive cables of the battery, detach the battery from its pan, lift it out from the battery well and replace with a new one. Attach the cables of the replacement battery appropriately, and assemble it in the battery well.
The BMW car battery is located under the carpeting towards the right side in the vehicle's trunk. Remove the carpeting completely. Then locate, remove and lift the cables of the old battery from their terminal posts using a crescent and open-end wrench. Remove the negative cable first. Ensure that the positive and negative cable ends do not come in contact with each other to prevent a short circuit in the vehicle's electrical system.
With a socket wrench, unbolt the old battery from its pan and take out the clips on the sides. Gently raise the battery out of its well using the handle straps or by covering with an old cloth piece. Position the replacement battery in the well keeping the posts in the same direction.
Then, reattach the clips to hold the new battery in place and connect the red and black cables to the positive and negative posts, respectively. Finally, replace the carpeting and test the new BMW battery,