Siemens alarm 2101: NCK battery alarm
SINUMERIK NCK general alarm · Siemens 840D/810D powerline
What it means
The undervoltage monitoring of the NCK backup battery (response threshold roughly 2.4-2.6 V against a 3 V nominal cell) has responded while the control was in cyclic operation. The SRAM contents are still intact, but the battery must be replaced soon or machine data will be lost at the next power-off. If replaced without interrupting power, or within about 30 minutes of switch-off while a buffer capacitor holds the SRAM, no data is lost.
Likely causes
- Backup battery discharged after 1-3 years of service
- Battery previously ignored when alarm 2100 prewarning appeared
- Poor battery holder contact or corroded connector
- Battery installed dead-on-arrival or beyond shelf life
Triage note: Replace battery with NCK powered up, or within ~30 min after switch-off, then clear alarm with Delete key or NC START; back up NC/PLC/drive data first.
Replacement parts
We supply the following units for this alarm — tested, warranty-backed:
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6FC5247-0AA18-0AA0
battery · Primary suspect
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CR1/2AA 3V lithium with plug (Siemens 575332TA type)
battery · Common cause
Need the part urgently?
Send us alarm 2101 with your machine details — typical RFQ turnaround is 24–48h.