Honeywell 300-10342 PROSIXC2W Replacement Battery 3.7V 3400mAh

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

This 3.7V 3400mAh Li-ion cell replaces OEM part 300-10342 in the Honeywell Home PROSIXC2W and PROSIXC2W Hardwired-to-SiX Wireless Converter. It sits inside the control panel and supplies backup power when mains power is interrupted. Without a functional cell, the panel cannot maintain zones, alerts, or programming during an outage.

• PROSIXC2W and Hardwired-to-SiX Converter compatibility: Both variants use the same 3.7V single-cell architecture and the same 300-10342 connector footprint. The panel BMS reads cell state via the same charge circuit on both models, so one cell covers either unit.
• Bench tested on actual hardware: We ran the cell through charge acceptance on the PROSIXC2W charge circuit and confirmed the BMS completed float charge without fault codes. Capacity measured within 3% of the rated 3400mAh at full cycle.
• Post-installation panel charge window: Do not run a zone diagnostic immediately after swapping the cell. The PROSIXC2W charge circuit needs 24 to 48 hours to bring the new cell to full float. Running a test before that window closes can trigger a false low-battery warning that clears on its own once charge completes.

Why the PROSIXC2W drops its programming during a power outage after a battery swap

The panel writes zone configuration and user codes to volatile memory backed by the 3.7V cell. If mains power fails before the new cell has been accepted by the BMS — typically within the first 48 hours — the panel may not draw enough current from the cell to hold that memory. The result is a reset to factory defaults or partial loss of enrolled sensors. Let the panel sit on mains power for a full 48-hour conditioning period before testing backup behaviour. After that window, the BMS transitions to maintenance float and the cell voltage stabilises above 3.6V — sufficient to protect memory during outages.

Panel reporting low battery fault minutes after new cell installed

This is a BMS reporting issue, not a cell defect. The PROSIXC2W reads cell state-of-charge immediately on power-up, and a freshly installed cell that hasn't yet been charged by the panel's internal circuit will read below the panel's threshold — usually under 3.5V. The fault clears automatically once the charge circuit brings the cell above that threshold, which takes between 24 and 48 hours on mains power. No action is needed beyond leaving the panel powered — the fault should clear without any manual reset once the cell reaches approximately 3.7V float.