Don't make the understandable mistake of looking under the bonnet for the battery when you're going to change one in a Mini Cooper S. These sporty little cars house the battery in the boot, under the luggage compartment. As is the case with all car batteries, the Mini Cooper's electronics and starter are powered from the device. Be sure to replace it with the proper-sized battery (243 cm x 175 cm x 190 cm) for the car.
Park the car and pull on the hand brake. Turn off all electric systems in the car. Open the boot/hatchback and pull up on the floor's handle to expose the battery and storage area under the luggage compartment.
Remove the red/positive cable from the old battery using the pliers or adjustable spanner. Take care to not strip the terminal.
Remove the black/negative cable last. If the cable connections are corroded, wash them off with an rust removing fluid and rag. The acid in the fluid cleans the battery corrosion from the cable fixtures.
Remove the old battery and place the new one in the same housing area in the car.
Attach the black/negative cable first. Attaching the black helps prevents shorts or surges in the system because it is also the ground wire for the car and battery. Attach the red/positive and then close the storage area and hatchback.
Start the car to test the battery. Give your Mini a run out to ensure the new battery fully charges.