On my Astra 53 plate, the key fob only works now and then?

Astra 53 plate key fob doesn't work properly, don't want to pay main dealer prices as they may sting me for reprogramming, etc. May be the battery? If so how do I get to battery? Does anyone know if the reprogramming part can be done like the 2000 year astra's, ignition to position II and press lock?
Any suggestions?
Thanks guys.
Regards,
Tony.