FOXLINK FLK644A Cable Modem Replacement Battery 10.8V 2200mAh

FOXLINK FLK644A — 10.8V Li-ion Replacement Battery

This is a 10.8V, 2200mAh Li-ion replacement battery for the FOXLINK FLK644A cable modem backup unit. It slots into cable modems that use the FLK644A cell to maintain power during an outage. When the original battery degrades, the modem loses its ability to sustain VoIP and data connections when mains power drops.

• FLK644A platform fit: Cable modems in this series share a common battery bay, voltage rail, and BMS handshake tied to the FLK644A cell spec. Any cell outside that voltage window will be rejected by the modem firmware before it ever gets used for backup.
• Bench tested on actual hardware: We cycled this cell through a full charge and discharge sequence. The BMS accepted the new cell after a complete charge cycle and reported battery status correctly to the modem firmware — no fault flags after the initialisation window closed.
• Post-install charge window: Cable modem firmware runs an internal battery acceptance check after a new cell is installed. Connect the modem to mains power and allow at least 4 hours of uninterrupted charging before running any self-test or expecting backup function to activate.

Battery self-test failing after a new FLK644A cell is installed

Cable modem firmware does not immediately trust a new battery. It runs a self-test sequence that checks both charge state and BMS communication before marking the battery as active. If the cell hasn't reached a full charge state, the test fails — not because the battery is faulty, but because the firmware won't accept a partial charge as valid. Allow 4 hours of continuous mains power after installation before triggering any self-test. The target charge voltage for the FLK644A cell is 12.6V at full capacity.

Modem showing a battery error light 24 hours after replacement

A battery error indicator within the first 24 hours is a firmware timing issue, not a dead cell. The modem's power management controller re-initialises its battery profile after every swap, and that process can take up to a full day to clear. If the error LED persists beyond 24 hours, check that the battery connector is fully seated — a partial connection causes intermittent BMS signal loss, which the firmware logs as a battery fault. Re-seat the connector and allow another full charge cycle before concluding the cell is defective.