Johnson Controls MS-BAT1020-0-SUB PLC Replacement Battery 3.6V 700mAh

Johnson Controls MS-NCE2566-0 — 3.6V Ni-MH Replacement Battery (MS-BAT1020-0-SUB)

This is a 3.6V, 700mAh Ni-MH rechargeable cell for the Johnson Controls MS-NCE2566-0 Network Control Engine. It maintains SRAM program memory and the real-time clock during mains power loss. Without a healthy cell, the controller loses its operational parameters the moment facility power drops.

• MS-NCE2566-0 memory retention circuit: The NCE2566-0 routes the backup cell through a dedicated retention rail that powers SRAM and the RTC independently of the 24V bus. The cell must hold above the SRAM retention threshold — approximately 3.0V — to keep that rail live. A depleted or absent cell drops the rail and the program is gone before the main supply even recovers.
• Bench tested on actual hardware: We cycled this cell on the float charge circuit and confirmed the BMS accepted the charge profile without fault flags. Cell voltage settled at rated output after a full charge cycle and the retention rail stayed stable throughout a simulated mains-loss event.
• Hot-swap procedure for the NCE2566-0: Always replace this cell while the controller is powered on and in RUN mode. The NCE2566-0 has no internal capacitor buffer — the instant the cell is disconnected with the PLC off, the SRAM rail collapses and program memory is erased. A powered swap keeps the retention rail live for the seconds it takes to seat the new cell.

Why the NCE2566-0 loses program memory during a battery swap

The MS-NCE2566-0 uses static RAM for program storage, not flash. SRAM requires continuous voltage to hold data — the moment the backup rail drops, every stored parameter is gone. Unlike some PLCs that include a hold-up capacitor to bridge a cell swap, the NCE2566-0 relies entirely on the battery for retention voltage. If the controller was off or the cell was pulled while unpowered, a full program reload from the connected programming device is the only recovery path.

Battery alarm on the NCE2566-0 not clearing after a new cell is installed

The NCE2566-0 does not auto-clear a low-battery alarm once a new cell is seated — the fault flag stays latched in the controller's diagnostic register until it is manually acknowledged. Open the Metasys programming interface, navigate to the battery alarm object, and reset the flag from there. If the alarm returns immediately after reset, check that the cell voltage has risen above 3.3V — a new cell shipped in storage state may read low for the first few hours on the float charger before reaching full voltage.