Gateway support told me I could do this but since my system (Gateway model M-6848 running Vista Home Premium) is no longer under warranty (or it's some kind of state secret), they won't inform me of the procedure to operate it on A/C alone without the battery installed.
I have already attempted to remove the battery when the system is plugged in and running the OS and it just shuts down immediately. It also won't boot without the battery installed so I am a bit concerned about the answer I got from Gateway.
I have considered disabling the Microsoft ACPI-Compliant Control Method Battery from the Device Manager but would like a second opinion before I do.