Save yourself a few quid by replacing the battery in a dead key fob.
The unit started behaving erratically and then failed when I returned to the car at the local supermarket. Had to use the key and this set off the alarm which resulted in a few suspicious looks!
Enquiries revealed that a replacement would set me back over £75 I decided to do a bit of DIY.
The unit is sealed but with careful use of a Stanley knife it can be opened and then it is a relatively simple soldering job.
The battery you need is a Panasonic VL2330-1HFE rechargeable lithium which are readily available on eBay for approx £6.00 delivered. Tattoos - Why would you choose to look like the wall of a public toilet?

Sorry forgot to mention that superglue was used to join the 2 halves again. Tattoos - Why would you choose to look like the wall of a public toilet?

Great news - you managed to save a lot og quids

Several of us did this over 18 monhs ago - you'll find loads of info and pictures from a search.

Keep up the good work and post those DIY fixes  2002 Honda VFR800
2002 Toyota Celica 140 Silver (mid life crisis - again!)
2007 FL2 GS Manual Army Reconnaissance Green + freel2.com sticker
2004 Toyota Celica 140 Black - Gone
2000 Toyota Celica 140 Silver - Gone
1998 Toyota Celica ST Pearl Green - Gone
1996 Nissan Primera 1.6 - Gone
1994 Rover Montego 1.6 Auto - Gone