Emerson CPU310 Replacement Battery 3V 3300mAh

Emerson CPU310 / CMU310 — 3V Lithium Replacement Battery

This is a 3V 3300mAh lithium cell for the Emerson CPU310 and CMU310 programmable logic controllers. It backs up the real-time clock and SRAM memory retention when main power is lost or the controller is disconnected. Dimensions are 73.68 × 24.80 × 9.60mm — confirm fitment against your existing cell before ordering.

• CPU310 and CMU310 fitment: Both controllers share the same battery bay geometry, voltage rail, and memory-retention circuit. One cell covers either unit without modification.
• Bench tested on actual hardware: We cycled this cell through the CPU310's float-charge circuit and confirmed the BMS accepted the cell without fault flags. Open-circuit voltage stabilised within expected range after a full charge cycle.
• Hot-swap procedure — mandatory: Always replace this battery with the CPU310 powered on and in RUN mode. The SRAM holding the controller program is volatile — cut power to the cell for even a few seconds while the PLC is off and the program is gone. If the PLC was off during the swap, reload the program from your programming device before restarting.

PLC battery alarm not clearing after a confirmed good installation

Fitting a new cell does not automatically clear a battery alarm on the CPU310. The alarm is a latched flag in the controller's diagnostic register — it stays active until you acknowledge it in the programming software. Connect your programming device, navigate to the diagnostics or status buffer, and reset the battery fault flag manually. The controller will not return the alarm after reset as long as the new cell reads above the low-battery threshold, typically around 2.7V.

New cell reading lower than 3V immediately after fitting

Lithium backup cells ship at a reduced storage voltage — often 2.85V to 2.95V — to slow self-discharge during transit and warehousing. This is normal and does not indicate a faulty cell. Once seated in the CPU310 and connected to the float-charge circuit, the cell voltage climbs to the rated 3V within a few hours. If voltage has not recovered after 24 hours on a powered controller, reseat the cell and check the battery connector pins for corrosion or bent contacts.