This module is imbedded in a specially-enlarged replacement cover. Installation is performed by replacing the original cover, together with wiring the GD-04A module to the GD-04 circuit board via the corresponding connector. The backup battery requires approx. 72 hours to be fully charged. The battery provides approx. 12 to 24 hours of backup operation, depending on the output relay state and on the GSM signal strength (as with any GSM device, David’s consumption is higher in places with a low signal level as the transmitter power has to be increased).