Apparently there are 2 types of key for the R53 and mine had a rechargeable that is not suitable to replace - I think it can be done but a lot of reports suggest the keyfob is liable to break as you open it as they were never designed to be open. Obv I'm only going on what I've read but there are a lot of similar reports - most post's advised buying a new fob if the battery gives up the ghost.
No issues since thankfully