TYCO 2XER18505M Wireless Siren Replacement Battery 3.6V

TYCO PG9901 / Wireless Indoor Siren Res Fire — 3.6V Li-SOCl2 Replacement Battery (2XER18505M)

This is a 3.6V 16000mAh lithium thionyl chloride cell built to replace the 2XER18505M battery in TYCO wireless indoor fire and burg sirens. It fits the PG9901, Wireless Indoor Siren Res Fire, and Burg Siren models. Once installed, it restores backup power so the siren can sound during a mains outage or fire event.

• PG9901 and Burg Siren compatibility: These three models share the same 3.6V single-cell architecture, 2XER18505M connector footprint, and BMS voltage threshold. One cell covers all three without modification.
• Bench tested on actual hardware: We ran the cell on a PG9901-class siren board under simulated alarm load. The BMS accepted the new cell within normal float window and the panel cleared the low-battery flag after the required conditioning period.
• Post-install panel reporting on TYCO siren platforms: Do not run a zone or siren test immediately after fitting this cell. TYCO wireless siren panels typically need 24 to 48 hours on float charge before the BMS reports full capacity. Testing before that window expires will trigger a false low-battery fault on the panel display.

Alarm panel showing low battery hours after installing new cell

Li-SOCl2 cells ship in a partially passivated state. The internal oxide layer on the lithium anode briefly suppresses voltage output until the cell begins delivering current to the circuit. TYCO siren panels sample battery voltage during this passivation window and interpret the suppressed reading as a depleted cell. The panel will clear the fault on its own once float charge stabilises — this normally happens within 24 to 48 hours of continuous connection. No panel reset is needed; check again at the 48-hour mark and confirm the voltage reads above 3.5V at the terminal.

Siren not sounding on activation test after battery swap

Some TYCO wireless siren units enforce a 30 to 60 second charge-stabilisation delay on a freshly installed cell before allowing the sounder to fire. During this window the panel may acknowledge the alarm trigger but the siren stays silent. This is a BMS-level hold, not a wiring fault or a defective cell. Wait at least 60 seconds after fitting the battery before running any test activation. If the siren still fails to sound after that delay, check that the battery terminal contacts are fully seated and that the housing cover is closed enough to release any built-in tamper switch.