Siemens Simatic S-7 3V Replacement Battery A5E00331143 800mAh

Siemens Simatic S7 — 3V Li-MnO2 Replacement Battery (A5E00331143)

This is a 3V, 800mAh lithium manganese dioxide cell for the Siemens Simatic S7 programmable logic controller. It fits both the Simatic S-7 and Simatic S7 controller variants. The battery backs up the real-time clock and SRAM memory when the primary power supply is removed.

• Simatic S7 memory retention: The S7 controller uses this cell solely to hold SRAM data and RTC state during mains power loss. The cell does not run the CPU — it only sustains the memory voltage rail when the power supply drops out. Voltage compatibility and the physical form factor match OEM part A5E00331143 directly.
• Bench tested on actual hardware: We ran the cell under a continuous low-current drain replicating S7 SRAM standby draw. The BMS held stable output across the full test period, with no voltage dip below the 2.5V SRAM retention threshold.
• Hot-swap procedure on the S7: Always replace this cell with the PLC powered on and in RUN mode. Removing the old cell while the controller is de-energised will cause SRAM to lose all stored data immediately. A powered swap keeps the memory voltage rail live throughout the exchange.

SRAM retention voltage threshold on the Siemens S7

The S7's SRAM requires a minimum of approximately 2.5V to retain data. A fresh Li-MnO2 cell delivers a nominal 3V open-circuit, which gives comfortable headroom above that floor. As the cell ages and voltage sags, the controller reaches the threshold before the cell reads as fully depleted. This is why the S7 battery alarm typically triggers well before the cell measures zero — the controller protects SRAM by alerting early.

Battery alarm still showing after installing a new cell

The S7 battery alarm does not clear automatically once a new cell is fitted. The fault latch stays active until acknowledged manually inside the programming software — typically via STEP 7 or TIA Portal diagnostics. Open the hardware diagnostics view, confirm the new cell is recognised, then clear the fault flag. If the alarm returns within hours, check that the cell contacts are fully seated and measure voltage at the battery connector — it should read above 2.8V.