Applicable Systems
MicroLogix
CompactLogix
ControlLogix
PowerFlex
Symptoms
The controller's OK LED remains green but a minor fault is logged. The battery backup voltage is low, indicating that the battery needs replacement. The controller continues to operate normally.
Possible Causes
- Battery has reached end of life
- Battery was not replaced after the low battery warning
- Battery contact corrosion or loose connection
- Extended power-off period drained the battery
Troubleshooting Steps
- Step 1: Check the minor fault log in Studio 5000 for the battery low warning
Confirm the fault is a low battery warning (type 16#0011) - Step 2: Power down the controller and locate the battery compartment
Battery is accessible for replacement - Step 3: Remove the old battery and install a new one of the same type
New battery is installed with correct polarity - Step 4: Clear the minor fault in Studio 5000
Battery fault is cleared and no new battery warnings appear
How to Reset
To reset: 1) Replace the controller battery with a new one. 2) Clear the minor fault in Studio 5000 via Controller Properties > Minor Faults. Caution: Replace the battery while the controller is powered to avoid losing volatile memory contents.
Common Replacement Parts
- 1747-BA: Controller backup battery (Replace with the same catalog number; do not use substitutes)
Frequently Asked Questions
- Q: How often should I replace the PLC battery?
Typically every 2-3 years, but follow the manufacturer's recommendation. Replace proactively when the low battery warning first appears.
- Q: What happens if the battery dies completely?
The controller will lose its retained memory contents, including timer and counter accumulated values, when power is removed.
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Source: Rockwell Automation CompactLogix 5370 User Manual, Publication 1756-UM522
Category: PLC & VFD
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