Park on a flat, level surface in a safe place, put on the hand brake and take the keys out of the ignition (some vehicles may activate the central locking when replacing the battery, so keep the keys somewhere safe). Don’t forget to wear protective goggles and gloves, as car batteries contain acid which is highly corrosive.
Before replacing the battery make sure you’ve got all the PIN codes and settings for your electronic equipment such as radios and satellite navigation etc. Some modern vehicles have systems that need to be reset after the battery has gone flat or been disconnected. Check the owner’s handbook or an expert if you are unsure.
Open the bonnet and use the bonnet stay to keep bonnet open (Some vehicle’s bonnets may stay up on their own).
Locate the battery. They are normally under the bonnet, but they can also be in the boot or even under the seat. Again, check the owner’s handbook for more information.
Remove any plastic trims / covers from the battery.
Label the battery cables so that they don’t get mixed up. It’s important that you disconnect the negative connection before the positive, or you may cause damage to the vehicle’s electrical system.
Loosen and disconnect the negative cable clamp (normally marked with “ –“ (minus) ) and move the clamp away from the battery post.
Loosen and disconnect the positive cable clamp and move away from the battery post.
Remove any screws, clamps or bars holding the battery in place. Disconnect any vents that are attached and carefully lift the battery out of the vehicle. Remember that a car battery is quite heavy so you may need a helping hand.
Fit the new battery making sure the positive and negative posts are on the correct sides. Connect any vent pipes, screws, clamps or bars that hold the battery in place.
Remove any covers from the new batteries terminals.
Reconnect and secure the positive cable clamp (make sure the connection is as far down on the battery post as possible).
Reconnect and secure the negative cable clamp (make sure the connection is as far down on the battery post as possible).
You are now ready to start the vehicle.
Adopted from http://www.racshop.co.uk/car-battery/how-to-fit-a-battery.html