Volkswagen keys are all different but are put together practically the same for every key. The key is composed of three parts: the lower and the two upper pieces. The key is held together by pressure. Battery type varies between keys, but the common battery is a round, flat 1.5-volt battery. You need to change the battery as soon as the key remote stops working. You can buy the replacement battery at your local drugstore for around £3.
Pick up the key and locate the thin space between the upper and lower parts of the key. The connecting point is in the centre all the way around the key.
Place the blade of the screwdriver between the upper and lower parts of the key. Turn the screwdriver in either direction until the upper and lower parts separate.
Pull the upper and lower parts apart. Pull the two upper parts apart and use the blade of the screwdriver the pry the battery from the key. Place the new battery inside the key. Reassemble the key the opposite way that you took it apart.