About this replacement
AT&T DLC-200C — 7.4V Li-ion Replacement Battery (DL200-BAT-2S3P-002)
This 7.4V, 10200mAh Li-ion battery replaces the backup cell in the AT&T DLC-200C cable modem. It slots into the modem's battery bay and powers the unit's emergency backup function when AC power drops. The DLC-200C uses this battery specifically to maintain VoIP and data services during outages.
- DLC-200C backup system: The DLC-200C uses a 2S3P Li-ion pack to match its internal battery management bus. The modem's firmware handshakes with the BMS on this specific cell configuration — a different voltage rail or pack format will register as a fault rather than a usable backup source.
- Bench tested on actual hardware: We ran this pack through the DLC-200C's self-test sequence after a full charge cycle. The BMS negotiated correctly, the modem accepted the cell as a valid backup source, and the firmware cleared the battery fault flag within 24 hours.
- First charge on the DLC-200C: Leave the modem plugged into AC power for at least 4 hours after installing this battery before testing backup mode. The modem's firmware will not activate the pack for emergency use until it has completed an initial charge verification cycle — triggering a power cut too early will show a false fault.
Modem showing battery error after installation
The DLC-200C runs a firmware-level battery acceptance sequence when a new cell is connected. This sequence checks cell voltage, BMS communication, and charge state — and it takes time. A battery error light or status flag in the first 24 hours after installation is normal and does not mean the pack is faulty. Keep the modem on AC power and allow the full charge cycle to complete. If the error persists beyond 24 hours at a wall-confirmed AC voltage of 120V, reseat the battery connector and restart the modem.
VoIP calls dropping during power outage while internet stays up
The DLC-200C prioritises data traffic when operating on battery backup, and VoIP draws sustained higher current than a basic data connection. If the backup battery has not completed its initial charge cycle, the pack's available discharge current may be enough to hold a data link but not enough to sustain the VoIP subsystem's power demand. Charge the modem on AC for a full 4 hours before the next outage test. A fully charged 10200mAh pack at 7.4V provides enough capacity for both data and VoIP simultaneously.