JOHNSON Controls Metasys NU-BAT300-1 6V Replacement Battery

JOHNSON Controls Metasys — 6V Ni-CD Replacement Battery (NU-BAT300-1)

This is a 6V 1500mAh Ni-CD replacement for the JOHNSON Controls Metasys building automation controller battery. It fits the Controls Metasys and NU-NCM300-1 modules, where it maintains SRAM program memory and RTC data during mains power interruptions. Capacity is 1500mAh (9Wh), matching the original NU-BAT300-1 specification exactly.

• Metasys module compatibility: The Controls Metasys and NU-NCM300-1 share the same 6V battery rail, connector pinout, and BMS handshake requirement. Both modules draw from this cell to hold SRAM state and keep the real-time clock running when mains power drops.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a PLC backup load profile. The BMS accepted the cell without fault codes, float charge settled at the correct voltage, and SRAM retention held across a simulated mains-out event.
• Hot-swap procedure — critical for Metasys: Always replace this battery with the Metasys controller powered on and in RUN mode. Removing the cell while the controller is off will wipe SRAM — the full program will need to be reloaded from a connected programming device before the controller can resume normal operation.

Metasys battery alarm not clearing after a confirmed good installation

Installing a new cell does not automatically clear the battery alarm in Metasys. The alarm flag is stored in software and requires a manual acknowledgement step inside the Metasys programming or site director interface. Navigate to the alarm management panel and clear the battery fault event directly. Until that step is done, the new cell will function correctly but the alarm will continue to display regardless of actual battery condition.

New cell reading lower than 6V immediately after installation

Ni-CD cells ship in a partial storage state — typically 5.4V to 5.7V — to reduce capacity loss in transit. This is normal and does not indicate a faulty cell. Once installed in a powered Metasys controller, the float charge circuit will bring the cell up to its rated 6V within a few hours. Verify with a multimeter at the battery connector after four hours of controller-on time — the reading should be at or above 5.85V.