Guys i seriously would not open your keys up they are a sealed unit for a reason,, Factory original VR keys are the only ones that should ever be opened as they were designed to have the battery replaced,,, Every other model the battery is soldered in place an a replacement battery wont work as the remote was not designed to take a replacement item,, You can blow the circuit in the remote. Holden Factory batteries are slightly different to the batteries you buy at you local shop..
To save yourself the dramas just take the working key to a locksmith an get them to copy it onto a new head,, simple an easy to do takes all of 5min,, Holden will charge a bucket load for a new key last i checked was $180 for the key then ya gotta take it somewhere to get cut if you getting a whole new key, expect to pay around the $50 mark to get it cut then back to Holden for another $80ish to get it programed... A decent locksmith should be able to cut an program the key for around $100 to $130. again takes all of 10min if they a decent locksmith. To introduce the key to the car takes all of 30seconds its so simple...
To save yourself the dramas i seriously recommend not opening the heads,,, also before anyone says i have no idea what im on about iv been in the key industry for nearly 3 years and at my old job i specialized in automotive keys an not just Holden..