Hi, new R53 owner in peace!

I have a query about key fobs. the two that came with my both start the car fine but one doesn't open the doors etc. A bit of searching suggested that it could just be a flat battery in the key fob as it might have been the spare. are they cheap enough to get replaced as they look sealed. Has anyone had any replaced and got a good recommendation?

Also looking for a decent place to buy bits for the car too. Needs boot struts and a rear light glass. Anyone have any recommendations?