Low battery voltage in FANUC systems is a common issue. If not addressed promptly, it may result in data loss or home position offset. This article provides a detailed explanation of how to identify the alarm, the replacement procedure, and important precautions to help you resolve the issue quickly.
Alarm Recognition
NC System Battery (BAT Alarm): The alarm is indicated by a flashing “BAT” in the lower-right corner of the screen. Its function is to preserve SRAM data such as system parameters, machining programs, tool offsets, and coordinate systems. The risk is that if the power is cut off due to low voltage, all data will be lost, requiring a system reinstallation or data recovery.
Absolute Encoder Battery (APC Alarm): The alarm is indicated by a yellow flashing “APC” in the status bar. Its function is to store the absolute position data of the servo axes. The risk is that the home position will be lost after a power outage, requiring the machine to return to zero upon startup. When the voltage is low, the APC flashes and DS307/307 alarms are triggered (battery at 1/2 capacity); when the voltage reaches 0, the 306 alarm (battery voltage 0) and 300 alarm (need to return to zero) are triggered; the ALM flashes, indicating that the origin has been lost.
Quick Reference Chart
| Battery Type | Voltage Status | System Display | Risks |
|---|---|---|---|
| NC System Battery | Low Voltage | BAT flash | Data is about to be lost. |
| 0V | SYST-035, Data lost | Parameters/programs need to be reinstalled. | |
| Absolute Encoder Battery | Low Voltage | APC flash, DS307 | The origin is about to be lost. |
| 0V | 306, 300, ALM flash | The origin has been lost; you must reset to zero. |
Processing Steps:
Preliminary Preparations (Required): Back up data, including NC system backup parameters, programs, tool offsets, and coordinate systems; record the current position or perform a home operation before replacing the encoder battery. Prepare the necessary tools; an original battery is required. Use a multimeter set to the DC voltage range to measure the voltage across the battery terminals. Check for false voltage readings caused by low temperatures; if the alarm clears after warming up, the issue is resolved; if the alarm persists, it indicates a hardware problem. If the battery has poor contact, clean the battery compartment, unplug and reinsert the battery, and verify that the positive and negative terminals are correctly connected. When a BAT alarm occurs, check parameters 3105#0 (BAC) and 3190#0 (BAL) to ensure battery detection has not been disabled.
Replacing the NC System Battery (BAT Alarm): Please have a lithium battery ready in advance (stock specification: A02B-0323-K102).
- Turn on the power to the machine tool (control unit) for approximately 30 seconds, then turn it off.
- Remove the lithium battery from the back of the control unit by grasping the latch on the battery and pulling it forward while releasing the retaining clips on the battery compartment.
- Insert the prepared lithium battery and press it in until the battery’s retaining clips engage with the housing; ensure the latch is securely locked in place.
Important Notes
Warning: Failure to replace the lithium battery correctly may result in an explosion. Do not replace it with any battery other than the specified lithium battery (A02B-0323-K102).
Note: Steps 1 through 3 must be completed within 30 minutes. Please note that if the battery remains disconnected for too long, the data stored in the SRAM will be lost. Before proceeding with the replacement, be sure to back up all data stored in the SRAM; this will make it easier to recover the data should it be lost.