The ELK P624 Power Supply and Battery Charger requires its own ELK TRG1640 Transformer and a separate 12V Seal Lead Acid Battery. The separate Battery will connect to the battery leads on the P624 and provide battery backup to the devices the P624 is powering. IF you are trying to power an M1 Bus Device (for example a keypad, input/output expander, serial port expander) from the P624 you Must Connect a Common DC Negative (single wire) from the DC NEG on the P624 to any NEG terminal on the M1.