About this replacement
Denso 410076-0041 — 3V Li-MnO2 Replacement Battery
This 3V lithium manganese dioxide cell replaces the backup battery in the Denso 410076-0041 PLC. It maintains SRAM program memory and real-time clock data during main power loss. Capacity is 1500mAh (4.5Wh) — matched to the original cell specification.
- 410076-0041 PLC fit: This controller uses a dedicated 3V Li-MnO2 cell to hold the SRAM voltage rail above the retention threshold and keep the RTC ticking when mains power drops. The cell dimensions — 34.50 × 16.80 × 16.80mm — match the original battery bay without modification.
- Bench tested on actual hardware: We confirmed the cell stabilises at the correct float voltage on the PLC's backup rail and that the BMS handshake clears the low-battery alarm flag after installation with the controller powered on.
- Hot-swap is mandatory on this controller: Never remove the old cell while the Denso PLC is powered off. Always swap the battery with the controller live and in RUN mode. If the PLC was off during the swap, SRAM contents are gone — a full program reload from the programming device is required before the controller can resume normal operation.
Why the Denso 410076-0041 loses program memory after a battery swap
The 410076-0041 holds its ladder logic and configuration in volatile SRAM. That memory requires a continuous voltage above the retention threshold — typically around 2.0V — to survive. The moment that voltage drops below the threshold, the SRAM contents are erased. Removing the backup cell while the controller is powered off removes the only voltage source sustaining that memory, so the wipe is instant. A hot-swap — cell removed and replaced while the PLC is live — keeps the SRAM rail above threshold throughout the procedure.
Battery alarm still showing after a confirmed good installation
The low-battery alarm flag on this controller does not clear automatically when a new cell is fitted. It is a latched fault that must be manually reset in the programming software after installation. Connect to the PLC via the programming device, navigate to the diagnostic or fault log screen, and clear the battery fault flag from there. If the alarm reappears within days of a fresh cell, check enclosure temperature — an ambient above 40°C can accelerate self-discharge fast enough to re-trigger the alarm before the next maintenance cycle.