About this replacement
Cisco CP-7921G Unified — 3.7V Li-Polymer Replacement Battery (74-4957-01)
This is a 3.7V, 1200mAh Li-Polymer battery for the Cisco CP-7921, CP-7921G, and CP-7921G Unified wireless IP handsets. It slots into the rear battery compartment and restores full wireless operation when the original cell can no longer hold a charge. OEM part numbers covered: 74-4957-01, 74-4957-01 Rev. C1, and 74-4958-01.
- CP-7921 series compatibility: The CP-7921, CP-7921G, and CP-7921G Unified share the same battery bay dimensions, connector pinout, and 3.7V supply rail — all three accept this cell without modification.
- Bench tested on actual hardware: We ran this battery through charge and discharge cycles on a CP-7921G unit. The BMS accepted charge from the Cisco base station without triggering a fault condition, and voltage under RF transmit load stayed within the handset's operating window.
- First charge on the CP-7921G base station: Place the handset in the charging cradle immediately after fitting this battery and leave it for a full charge cycle before using it. Li-Polymer cells shipped in partial-charge storage state need one complete charge before the battery gauge calibrates correctly on this handset.
Talk time shorter than expected after fitting a new CP-7921 battery
A new Li-Polymer cell arrives partially discharged after storage. The CP-7921G's onboard fuel gauge reads this partial state and may underestimate remaining capacity for the first few cycles. Run two or three full charge-and-discharge cycles through the base station before judging actual capacity. After that, the gauge recalibrates and reported capacity stabilises at the rated 1200mAh.
CP-7921G loses DECT pairing after battery replacement
Removing the battery completely cuts power to the handset's volatile memory, which can clear the stored DECT pairing link on some firmware versions. When the handset powers back on with no base association, it sits idle and will not connect calls. Re-register the handset to the Cisco Unified Communications Manager following the standard DECT re-pairing procedure in your site's phone administration console. Confirm registration by checking the handset displays a signal icon and extension number at idle.