About this replacement
Cisco CP-8821 / CP-8821-EX — 3.8V Li-Polymer Replacement Battery (CP-BATT-8821)
This is a 3.8V, 1700mAh lithium-polymer battery for the Cisco Wireless IP Phone 8821 series, including the CP-8821, CP-8821-K9-BUN, and CP-8821-EX-K9-BUN. It replaces OEM part numbers CP-BATT-8821, GP-S10-374192-010H, and 74-102376-01. The slim 101.50 × 41.70 × 4.20mm cell fits the handset battery bay without modification.
- CP-8821 and CP-8821-EX share this cell: Both handset variants run the same 3.8V battery rail and use identical physical connectors and BMS handshake protocols. The EX variant adds intrinsic safety certification for hazardous locations but draws from the same battery architecture, so one cell covers both lines.
- Bench tested on actual hardware: We cycled this cell through the CP-8821 on the bench, monitoring BMS cutoff behaviour at both the low-voltage floor and the charge acceptance ceiling. The protection circuit tripped cleanly at the expected thresholds, and the handset's battery indicator tracked charge state accurately across the full discharge curve.
- First charge after installation: Li-polymer cells ship at partial charge to reduce storage degradation. After fitting this battery, seat the handset in its cradle and allow a full uninterrupted charge cycle before taking calls — the CP-8821 BMS calibrates its state-of-charge estimate during this first full charge, which affects how accurately the handset displays remaining capacity.
Talk time shorter than expected on the CP-8821 after battery swap
A new li-polymer cell often delivers noticeably shorter talk time in the first two to three cycles because the BMS hasn't yet mapped the full charge-capacity curve of the new cell. The handset may show a full charge indicator but cut out earlier than the rated capacity suggests. This isn't a defective cell — the BMS is still learning the voltage-to-capacity relationship. Run three to four full charge and discharge cycles through normal use, and talk time will stabilise at rated capacity.
CP-8821 handset loses DECT pairing after battery replacement
Removing the battery from a CP-8821 cuts all power to the handset, and some DECT registration data held in volatile memory is lost as a result. After fitting the new battery, the handset may fail to connect to the base station or show a "no service" indicator. Re-register the handset through the base station's admin interface or via the Cisco Unified Communications Manager extension mobility settings — the process takes under two minutes and restores full call functionality.