VoIP Guy,
I am going to make the assumption that you are not a certified technician at this point. If you are not then I would suggest that you allow a certified technician to perform the swap of the battery for a couple of reasons.
1. They will be able to determine if you really need to swap it out or not.
2. They would have the proper tools to resolve any issues that may come up.
I am not saying that you couldn't do it, but if anything major goes wrong then you are going to need more help than can be provided by the forums.
If you still want to do it yourself then there is a little window of opportunity where there is still a charge on the circuit after you take out the old battery and when you put in the new one. I typically would verify the charge on the current battery to determine if it is truly dead or not, but that is just me. Once you take the battery out you need to put the new one in immediately or the database could default on you. If that is the case then you will need to get into the system with either a serial cable or via the NIC. The default IP Address is 192.168.200.201/24, but you could also try using whatever is in there currently as well; as I said some odd things can happen.
Are you positive that you don't have a CPS on your site?
Thanks,
TE