I changed mine after posts from Poundy and Jberks. I found it easier to remove the last few clips/bolts and remove the entire wheel arch cover which...
I fell off my boat. As soon as I managed to scramble back on board, I removed the battery and dunked the fob parts into a mug of fresh water (twice)....
After my incident involving sea water, my battery needed replacing every few weeks. I bought an empty Smart car key fob, put spare batteries in there...