NVB272

Hi I am not an installer but wanted to ask a question, I have an Ademco Galaxy 16plus CP171 That was installed by the previous owner, when who knows. Some time ago i fitted new sockets-turning the power off obviously then then turning alarm from panel, however when i cut the power there is no power to panel. There are 2 boxes that contain batteries-do i change both? as i have no idea how old they are-it also says that they are rechargeable.