Replacement key - remote fob

looks like my remote "open" button has stopped working. I have seen lots of ad's for the fobs on ebay so i'm bound to get the wrong type.

is there anything i need to look out for when i buy a replacement one?

Make sure the part number ties up with the one you have (its inside the key).

It might be worth checking the battery spring terminals, as I thought mine had given up but it turned out i'd mashed the terminals when fitting a new battery