Hertz 286 PLC Backup Compatible Battery 3.6V 2700mAh

Hertz 286 / PC286 / AT / XT Series — 3.6V Li-MnO2 Replacement Battery

This is a 3.6V, 2700mAh Li-MnO2 cell for Hertz 286, AT, PC286, and XT series programmable logic controllers. It maintains SRAM program memory and real-time clock function when the main power supply is absent. Voltage and chemistry match the original cell specification for these controllers.

• 286, AT, PC286 and XT compatibility: These four models share the same 3.6V backup rail, physical cell format, and connector footprint. The BMS in each unit draws from this cell only when mains power drops — the cell sits on a float circuit the rest of the time.
• Bench tested on actual hardware: We ran this cell at 3.6V nominal against the controller's backup draw profile. The BMS accepted the cell without fault codes, and SRAM retention held across simulated mains-loss events at the expected voltage threshold.
• Hot-swap is mandatory on these controllers: Never remove the old cell while the PLC is powered off. Always replace the battery with the controller powered on and in RUN mode. Swapping with power off clears SRAM instantly — the program is gone and must be reloaded from a connected programming device.

PLC losing program memory after battery swap

SRAM on these controllers holds program data only as long as voltage stays above the retention threshold — typically around 2.8–3.0V for this cell chemistry. If the old cell is removed while the controller is off, SRAM voltage collapses within seconds and all user program data is lost. The RTC also loses its timestamp at the same moment. The only recovery is a full program download from the original project file on the programming device, followed by manually resetting the clock in the software.

Battery alarm not clearing after a confirmed good installation

On these controllers, the low-battery alarm flag is written into a status register — it does not clear automatically when a fresh cell is fitted. Even with a new 3.6V cell sitting correctly on the float circuit, the alarm stays active until you clear it manually in the programming software. Connect the programming device, navigate to the diagnostic or status register for the battery flag, and reset it explicitly. If the alarm returns within a short time, check the cell is seated fully and the connector has no oxidation on the contacts.