AT&T DLC-200C Cable Modem Replacement Battery 7.4V 7800mAh

AT&T DLC-200C — 7.4V Li-ion Replacement Battery (DLC-200 / DL200-BAT-2S3P-002)

This 7.4V, 7800mAh Li-ion battery is the backup power cell for the AT&T DLC-200C cable modem. It sits inside the modem chassis and takes over when mains power drops, keeping the modem alive long enough to maintain active calls and allow connected devices to shut down cleanly. Capacity sourced from product data: 7800mAh (57.72Wh).

• DLC-200C modem fit: The DLC-200C uses a 2S3P lithium cell pack with a specific connector and BMS handshake tied to the modem's firmware battery-management loop. This pack matches that configuration — same cell arrangement, same connector, same voltage rails the modem firmware expects to see during its charge and self-test cycles.
• Bench tested on actual hardware: We ran this pack through the DLC-200C charge controller and confirmed the BMS negotiation completes correctly. The modem accepted the pack, began the charge cycle without error flags, and the self-test sequence passed after a full charge cycle.
• First-charge protocol for cable modem backup cells: After installing, leave the modem plugged into mains power for at least 4 hours before testing backup function. The DLC-200C firmware gates backup activation on a completed charge cycle — pulling mains before that window causes the modem to report the battery as unavailable, even though the pack is functional.

Battery self-test failing after swapping the DLC-200C pack

The DLC-200C runs an automated self-test sequence to verify backup battery health. With a new pack installed, this test almost always fails if triggered too soon. The modem's firmware checks for a minimum state-of-charge threshold before it marks the battery as ready — a fresh pack straight from storage typically reads between 3.6V and 3.8V per cell, which falls below that threshold. Allow 4 hours of uninterrupted mains charging, then let the modem trigger the self-test on its own schedule rather than forcing it manually.

Modem showing a battery error light for up to 24 hours after installation

A steady or blinking battery error indicator after installing a new pack does not mean the pack is faulty. The DLC-200C firmware takes time to accept a new cell — it monitors charge intake rate and voltage curve before clearing the error state. This process can take anywhere from a few hours to a full 24-hour charge period. If the error light persists beyond 24 hours of continuous mains power, pull the battery, verify the connector is fully seated, and reinstall — the contact needs to be flush for the BMS handshake to complete at 7.4V nominal.