I'm a girl, a proper girly girl - but my husband is a very good hobby mechanic. That said, he's not so good with electrics or electronics.
So I figured - I have a useless diamond key fob and it's going to cost me about £150 to get a new key and fob. What have I got to lose if I bust it open and have a go at the battery? So I bought a new one off ebay for a fiver. In the meantime and encouraged by a glass of wine, I started to cut the cover open with a craft knife. It was slow going, so I went to the kitchen and used a smooth carving knife. It opened easily.
The internal buttons were not working and everything else seemed in tact, so I started trying to detatch the battery from the connectors and they were firmly stuck on. I hacked and hacked. Then I noticed that the conductive thingy (copper wire spiral) was not looking very uniform, some of the copper wires were gapped. So it rubbed them with the back of my nail till they looked even. Et Voila! The internal buttons began to work. I folded the battery and connectors back together, glued the case back together and I have saved myself a small fortune.
Thanks again for the info and encouragement to give it a go