Cisco CP-7921 Replacement Battery 3.7V 2000mAh 74-4957-01

Cisco CP-7921G Unified — 3.7V Li-Polymer Replacement Battery (74-4957-01)

This 3.7V, 2000mAh lithium-polymer battery replaces the OEM pack in the Cisco CP-7921, CP-7921G, and CP-7921G Unified wireless IP handsets. It slots into the same battery bay and connects via the original latch cover. Capacity matches the product data at 7.4Wh — no spec inflation.

• CP-7921 and CP-7921G compatibility: All three variants — CP-7921, CP-7921G, and CP-7921G Unified — share the same battery bay geometry, connector pitch, and 3.7V rail. One pack covers the full range.
• Bench tested on actual hardware: We cycled this pack on a CP-7921G unit, confirming the BMS holds charge acceptance through the handset's internal charge controller without triggering a fault LED on the base station.
• First-charge protocol for Li-Polymer IP handsets: The CP-7921G uses a trickle-charge circuit in the base that tops the Li-Polymer pack slowly. Seat the handset in the base immediately after install and leave it undisturbed for a full charge cycle before pulling it into active use — this lets the BMS calibrate its state-of-charge registers correctly.

Why the CP-7921G base station shows a charge fault after a battery swap

A replacement Li-Polymer pack sitting in a warehouse often arrives at a storage voltage around 3.5V or lower. The CP-7921G base checks the pack voltage before enabling its charge circuit — if the pack reads below the acceptance threshold, the base logs a fault and stops charging. This is a protection feature, not a defect. Seating the handset, waiting 60 seconds, then reseating it gives the base controller a second handshake attempt, which usually clears the fault once it detects a valid cell voltage. If the fault persists, leave the handset seated for 15 minutes — the trickle pre-charge will pull the pack voltage up to the acceptance window.

Handset loses DECT pairing after battery replacement

Removing the original battery cuts power to the CP-7921G's volatile memory, which can drop the stored DECT pairing data. This is a known behaviour on this handset — not a fault with the replacement battery. Re-register the handset to the Cisco Unified Communications Manager via the Settings menu under Network Configuration. Once re-registered, the handset pairs normally and holds the pairing across subsequent battery swaps as long as the new pack stays above 3.0V during storage.