Honeywell WEB-201 JACE-300E Replacement Battery 12V 300mAh

Honeywell Vykon JACE-300E / JACE-600E — 12V Ni-MH Replacement Battery (WEB-201)

This is a 12V, 300mAh Ni-MH backup battery for Honeywell Vykon JACE-300E and JACE-600E controllers, as well as the JACE AX 600 Tridium Niagara and JEC-334. It holds SRAM memory and RTC data when mains power is lost. Physical dimensions are 56.50 x 30.20 x 19.40mm — confirm against the original cell before installing.

• JACE-300E, JACE-600E, JEC-334 compatibility: These controllers share the same backup battery architecture — the WEB-201 footprint, connector, and 12V Ni-MH chemistry are common across the series. The BMS float-charges the cell from the controller's internal rail, so chemistry match matters. Substituting a Li-ion or sealed lead-acid cell here will cause overcharge faults.
• Bench tested on actual hardware: We cycled this cell through full discharge and recharge on a JACE-series controller. The BMS accepted the cell without fault, float charge engaged within seconds of installation, and SRAM retention held through a simulated mains-out event. Voltage climbed from storage level to full charge within a few hours on the controller's float rail.
• Hot-swap procedure — critical for JACE controllers: Always replace this battery with the controller powered on and in RUN mode. The JACE has no capacitor bridge to hold SRAM during a cold swap. Pull the old cell while the controller is live, seat the new one immediately. If the unit was off during the swap, a full program reload from your engineering workstation is required.

Why the JACE controller loses its program after a battery swap

The JACE-300E and JACE-600E store their active Niagara AX program and configuration in SRAM. SRAM is volatile — it needs continuous power to hold data. When the backup cell is removed with the controller powered off, even briefly, that memory is gone. There is no flash fallback on these older JACE controllers the way there is on newer JACE-8 hardware. The fix is a full program download from your Workbench-connected PC after reconnecting power.

Battery alarm not clearing after the new cell is seated

The JACE does not auto-clear a battery alarm once a new cell is installed. The alarm is latched in software and must be acknowledged manually through the Niagara AX or Niagara 4 Workbench. Navigate to the Platform Administration view, open the battery status node, and acknowledge the active alarm there. If the alarm returns within 24 hours, confirm the cell voltage has risen above 13V on float charge — anything below that points to a faulty connection or a cell that shipped damaged.