Southwestern Bell FF4500 Replacement Battery 3.6V 1300mAh

Southwestern Bell FF4500 Series — 3.6V Ni-MH Replacement Battery

This is a 3.6V, 1300mAh Ni-MH rechargeable battery for Southwestern Bell cordless phone handsets. It fits the FF4500, FF5000, FF5500, and FF901 series. These models share the same voltage rail and physical pack format, making this a direct swap for a degraded original.

• FF4500 / FF5000 / FF5500 / FF901 compatibility: All four models run the same 3.6V three-cell Ni-MH pack with the same connector footprint and charge acceptance curve. The base station charges at a fixed trickle rate matched to this chemistry — no BMS handshake is required, but the voltage floor must be met on first seat.
• Bench tested on actual hardware: We cycled this pack through charge and discharge on the FF4500 platform. The base station accepted the battery without a fault light, and the handset held a stable RF carrier under normal cordless load. Capacity reaches rated output after three to five full conditioning cycles.
• First charge after installation: Place the handset in the base for a full 16 hours before first use. Ni-MH cordless phone packs ship in partial discharge and need a slow initial charge to reach rated capacity — a fast top-up will not do it.

Base station showing no charge or flashing error light on a new Ni-MH pack

Southwestern Bell base stations use a voltage threshold check before initiating the charge cycle. A new Ni-MH pack that has sat in storage can drop below 3.0V, which the base reads as a fault rather than a depleted cell. The fix is a brief trickle pre-charge — seat the handset, leave it for 30 minutes, then remove and re-seat it to trigger a fresh charge cycle. Once the pack climbs above the acceptance threshold, the base resumes normal charging without further intervention.

Range dropping mid-call after a battery swap

Reduced range after a swap usually points to voltage sag under RF transmit load, not a defective pack. Ni-MH cells that have not completed conditioning cycles deliver lower sustained voltage when the DECT transmitter fires. The handset reduces output power as voltage dips, which shortens effective range. Run three full charge-to-discharge cycles on the base — by cycle four, resting voltage should stabilise above 3.4V and range should return to normal.