I'm pretty sure you can just change the batteries on these, least you can if it's a system 3. There's a good website for datatool, just google it, and they give you quite a bit of info for these including a list of dealers that will be able to sort you out. It may well be something else though. Have you 'despiked' your alarm system?
AND.......I hope you've got your PIN programmed in
Lastly if you're really having problems with it drop me a PM and I'll let you have the details of a good mobile technician who can come and sort you out. Good luck, freekin' nightmare these things...