Southwestern Bell BP999 Cordless Phone Replacement Battery 3.6V 2000mAh

Southwestern Bell BP999 / BT999 Series — 3.6V Ni-MH Replacement Battery

This is a 3.6V, 2000mAh Ni-MH battery pack for Southwestern Bell cordless phone handsets. It fits the BP999, BT999, FTH916, FTH918, and nine additional models in the same series. Install it when the original pack no longer holds a charge or fails to power the handset off the base.

• BP999 / BT999 / FTH series compatibility: These models share the same 3.6V three-cell NiMH pack format, connector pitch, and physical footprint. The base station charges at a voltage rail matched to this chemistry — swapping in a Li-ion or different voltage pack will not charge correctly.
• Bench tested on actual hardware: We cycled this pack through charge and discharge on a cordless phone base station. The BMS accepted charge immediately from storage voltage, and the handset registered full signal strength throughout discharge testing.
• First-charge protocol for NiMH cordless packs: After installing, seat the handset in the base and leave it for a full 16 hours before first use. NiMH cells in cordless phones reach rated capacity only after a slow initial charge — skipping this step leaves usable capacity 20–30% below the 2000mAh rating on the first few cycles.

Base station charge light stays off or flashes error on a new NiMH pack

NiMH batteries discharge slowly during warehouse storage and can arrive below the voltage threshold the base station needs to initiate a charge cycle. Some Southwestern Bell bases use a delta-V detection circuit that won't start charging if the pack voltage reads too low. The fix is to seat the handset firmly in the base and wait — most bases will begin a trickle charge within 15–30 minutes once the circuit detects any response from the cells. If the light remains off after an hour, remove and re-seat the handset to reset the contact connection.

Range drops noticeably when the handset moves away from the base

The DECT radio in these handsets draws a short burst of current each time it transmits. If the NiMH pack voltage sags under that RF load — common in the first few charge cycles or in a partially discharged pack — the transmit power drops and effective range shrinks. This is not a handset fault. Run three full charge-and-discharge cycles to condition the cells, which tightens internal resistance and reduces voltage sag under load. After conditioning, the pack should sustain transmit voltage above 3.2V through the majority of the discharge curve.