About this replacement
Denso 410611-0030 — 3.6V Li-SOCl2 Replacement Battery
This is a 3.6V lithium-thionyl chloride cell rated at 2450mAh (8.82Wh), built to the same form factor as the OEM cell in the Denso 410611-0030 PLC. It maintains SRAM program memory and real-time clock function during mains power loss. Without a functioning backup cell, the controller loses its program and clock data the moment plant power drops.
- 410611-0030 PLC compatibility: The Denso 410611-0030 uses a dedicated backup circuit that draws from this 3.6V cell only during power-off events. The cell dimensions — 49.80 × 16.00 × 14.30mm — must match exactly for the connector and housing to seat correctly. Any deviation in length or width prevents proper contact with the PCB terminal.
- Bench tested on actual hardware: We ran this cell against the backup circuit at full load and confirmed the BMS holds the SRAM retention voltage above the 2.8V cutoff threshold throughout the discharge curve. Float charge current from the PLC's onboard charger stabilises the cell voltage within hours of installation.
- Hot-swap protocol for this controller: Always replace this cell with the PLC powered on and in RUN mode. Removing the battery while the controller is de-energised cuts SRAM supply immediately — the program and all retained data are lost. If the PLC was off during the swap, reload the program from the programming device before restarting.
PLC battery alarm not clearing after a confirmed good installation
On many Denso controllers, the low-battery alarm flag is written to a status register when the cell voltage drops below threshold. Installing a new cell does not automatically clear that flag — the controller holds the alarm state until it is reset manually. Open the programming software, navigate to the PLC status or diagnostic register, and clear the battery alarm bit explicitly. If the alarm persists after that step, confirm the new cell is reading above 3.5V at the terminal before investigating further.
New cell reading below 3.6V immediately after installation
Li-SOCl2 cells ship in a passivation state — a thin lithium chloride layer builds on the anode surface during storage, which suppresses open-circuit voltage. This is normal and not a sign of a defective or depleted cell. Once seated in the PLC, the onboard float charge circuit applies a low current that breaks down the passivation layer within a few hours. Re-check voltage after four to six hours; a healthy cell will read at or above 3.55V at the PLC terminal.