About this replacement
Epson RC420 EZ Module — 26.4V Ni-Cd Replacement Battery (22N-700AACL)
This is a 26.4V 800mAh Ni-Cd battery for the Epson RC420 EZ Module PLC backup system. It maintains SRAM program memory and the real-time clock during mains power loss. Part number 22N-700AACL matches the original cell specification directly.
- RC420 EZ Module compatibility: The RC420 EZ Module uses a dedicated backup rail at 26.4V to sustain SRAM and RTC circuits independently of the main logic supply. The cell must match this voltage exactly — a lower-rated pack will not hold the retention threshold under extended outage conditions.
- Bench tested on actual hardware: We ran this cell on the float charge circuit and confirmed the BMS accepted the charge handshake without fault. Voltage stabilised at rated level within the expected charge window and SRAM retention held through a simulated mains dropout test.
- Hot-swap protocol for the RC420: Always replace this battery with the RC420 controller powered on and in RUN mode. Removing the cell while the controller is off will wipe SRAM — your program and RTC data will be gone. If the PLC was off during the swap, reconnect your programming device and reload the program from backup immediately.
Why the RC420 EZ Module loses program memory after a battery swap
The RC420 keeps its ladder logic and variable data in SRAM, not flash. SRAM is volatile — it needs continuous voltage from the backup cell to hold data. The moment that voltage drops below the SRAM retention threshold, the memory clears. This happens in seconds when the battery is removed from an unpowered controller. The only recovery is a full program reload from a connected programming device using a saved project backup.
Battery alarm on the RC420 not clearing after a new cell is fitted
The RC420 does not automatically cancel a battery alarm once a new cell is installed. The alarm flag is written to a status register in the controller and stays latched until it is manually cleared in the programming software. Connect your programming device, navigate to the system status or alarm log, and reset the battery fault flag explicitly. After clearing, confirm the cell voltage is reading at or above the minimum retention threshold — typically around 22V on a freshly installed Ni-Cd at storage charge, rising toward 26.4V within a few hours on float.