Honeywell 300-10342 PROSIXC2W Replacement Battery 3.7V

Honeywell Home PROSIXC2W — 3.7V Li-ion Replacement Battery (300-10342)

This 3.7V Li-ion cell replaces the OEM 300-10342 backup battery in the Honeywell Home PROSIXC2W wireless security panel and the PROSIXC2W Hardwired-to-SiX Wireless Converter. Capacity is 2600mAh (9.62Wh). When mains power drops, this cell keeps the panel armed, communicating, and logging events.

• PROSIXC2W and Hardwired-to-SiX Converter compatibility: Both units share the same 3.7V single-cell backup architecture and the same 300-10342 form factor. The connector and BMS handshake are identical across both variants, so one part number covers both.
• Bench tested on actual hardware: We cycled this cell through simulated mains-loss events on a PROSIXC2W panel. The BMS accepted the cell without fault codes, held float charge correctly, and the panel cleared its low-battery condition within 48 hours of continuous charge.
• Post-install charge window for PROSIXC2W panels: Do not run a zone or siren test immediately after swapping the cell. The panel needs 24–48 hours on float charge before its BMS reports a full battery. Running diagnostics before that window closes will trigger a false low-battery event on the keypad.

Alarm panel showing low battery hours after installing new cell

The PROSIXC2W panel does not report battery status based on a voltage snapshot at install time. It monitors float charge accumulation over a conditioning window of 24–48 hours before updating its status register. A cell that reads 3.7V on a meter can still trigger a low-battery event on the keypad until that window closes. Leave the panel on mains power for 48 hours, then check status — the alert should clear without any manual reset.

Panel loses programming during a power outage after battery replacement

If the new cell has not completed its 48-hour conditioning cycle, the panel's backup capacity may be below the threshold needed to sustain memory and radio communication during a mains outage. The panel draws a brief high-current spike when it transitions to battery mode, and an undercharged cell can sag below the panel's minimum operating voltage under that load. This causes the processor to reset, wiping zone and user programming. Allow the full 48-hour float charge to complete before disconnecting mains power for any reason.