About this replacement
Honeywell Modicon Quantum — 3.6V Li-MnO2 Replacement Battery (TL-5902)
This 3.6V lithium-manganese dioxide cell replaces the TL-5902 backup battery in Honeywell Modicon Quantum PLCs and TC-PPD011 processors. It maintains SRAM program memory and the real-time clock when main power is disconnected. Capacity is 1200mAh (4.32Wh), matching the original OEM specification.
- Modicon Quantum and TC-PPD011 compatibility: Both platforms use the same 3.6V lithium cell on the CPU module to back SRAM and the RTC rail. The connector pinout and physical form factor — 26.00 × 16.60 × 14.50mm — match the factory slot without modification.
- Bench tested on actual hardware: We ran this cell against the Quantum CPU module's float charge circuit. The BMS accepted the cell without a fault condition, and SRAM retention voltage held steady above the 3.0V threshold throughout the test cycle.
- Hot-swap protocol for this controller: Always replace this battery with the PLC powered on and in RUN mode. Removing the cell while the controller is powered off clears SRAM — the program disappears and a full reload from the programming device is required. This is the single most common cause of unplanned downtime during routine battery maintenance on Quantum systems.
Why the Modicon Quantum CPU module triggers a battery alarm after a confirmed good install
The Quantum CPU does not clear the battery alarm automatically when a new cell is inserted. The alarm flag is latched in the controller's diagnostic register and must be manually acknowledged through Unity Pro or Concept programming software. Navigate to the CPU diagnostics screen, confirm the battery status bit has returned to normal, then reset the fault. If the alarm persists after reset, check that the cell is fully seated — the contact spring on older CPU modules can oxidise and drop the connection voltage below the detection threshold.
New TL-5902 cell reading below 3.6V on the Quantum's diagnostic screen
Li-MnO2 cells ship in a storage state and typically arrive between 3.2V and 3.4V. This is normal — the cell is not defective. Once installed, the Quantum's CPU float circuit trickle-charges the cell back to its nominal 3.6V, usually within a few hours of powered operation. If the voltage has not risen to at least 3.5V after 24 hours on a powered controller, reseat the cell and check the battery connector on the CPU module for corrosion or bent pins.