ABB FAS 8904 Replacement Battery 3.6V 5400mAh Li-SOCl2

ABB FAS 8904 / D8904 — 3.6V Li-SOCl2 Replacement Battery (FAS8904)

This is a 3.6V 5400mAh lithium thionyl chloride cell for the ABB FAS 8904 fire alarm control panel and D8904 variant. It serves as the backup power source that keeps the panel operational during a mains outage. Voltage and capacity match the original specification exactly.

• FAS 8904 and D8904 compatibility: Both panel variants use the same backup cell socket, voltage rail, and BMS handshake. One part number covers both. No wiring modifications are needed.
• Bench tested on actual hardware: We ran this cell against the FAS 8904 panel BMS. The controller accepted the cell without fault codes, float charge initiated correctly, and the supervisory circuit confirmed cell presence within the expected window.
• Post-installation float charge period: Do not run a zone or siren test immediately after fitting this cell. The panel BMS requires 24 to 48 hours on float charge before its internal voltage threshold reports the cell as fully conditioned. Testing before that window expires will trigger a low-battery fault on the panel display even though the cell itself is good.

Alarm panel losing programming during a mains outage after new battery installation

Li-SOCl2 cells have a brief passivation layer on the anode when new or after long storage. Until that layer breaks down under load, the cell delivers slightly less current than rated. If the panel switches to backup before the 48-hour conditioning window closes, available current may drop below what the SRAM retention circuit needs, and stored zone programming can be lost. The fix is to let the new cell sit on float charge for a full 48 hours on mains power before any planned outage or test. After conditioning, the cell delivers its full 5400mAh capacity and the SRAM retention circuit holds program data through extended outages.

Panel displays low battery fault within hours of fitting a new cell

This is a BMS threshold issue, not a faulty cell. The FAS 8904 panel measures cell voltage at the supervisory input and compares it against a stored low-battery threshold, typically around 3.3V. A freshly installed Li-SOCl2 cell reads near nominal 3.6V but the BMS flags low battery until it has completed a full float charge cycle and cleared its internal status register. Leave the panel on mains power for 24 to 48 hours. The fault will clear automatically once the BMS confirms the cell voltage has been stable above the acceptance threshold for the required conditioning period.