Xact B650 Cordless Phone Compatible Battery 3.6V 1200mAh

Xact B650 — 3.6V Ni-MH Replacement Battery

This is a 3.6V 1200mAh Ni-MH replacement battery for the Xact B650 cordless phone handset. It slots into the handset battery compartment and restores power to a unit that no longer holds a charge. Capacity figures are taken from product data — 4.32Wh total energy.

• B650 handset fit: The B650 uses a single-cell Ni-MH pack at 3.6V with a physical footprint of 50.43 × 42.54 × 14.40mm. Any replacement must match that voltage and form factor — the base station charges to a fixed termination voltage calibrated for Ni-MH chemistry, so swapping to a different voltage or chemistry will cause charge errors or no-charge states.
• Bench tested on actual hardware: We cycled this pack through the base station charger and confirmed the BMS accepted the charge handshake without triggering an error light. Charge current stayed within the base station's trickle and fast-charge windows across multiple cycles.
• First-charge conditioning for Ni-MH: After installing the battery, place the handset in the base for a full 16-hour charge before first use. Ni-MH cells in storage ship in a partially discharged state — a slow first charge lets the cells equalize and reach rated capacity. Skipping this step will produce shorter-than-expected talk time on early cycles.

Why the B650 handset shows a charging error with a new Ni-MH pack

DECT base stations detect battery presence by reading the pack's resting voltage. A new Ni-MH battery that has been in storage can sit below 3.0V — low enough that the base station's charge controller reads it as an absent or faulty pack and throws an error light. The fix is to briefly short-charge the pack at a low rate to push the resting voltage above the acceptance threshold, typically around 3.2V. Once the base station sees a voltage it recognises, normal charging resumes and the error clears.

Range dropping on the B650 shortly after a battery swap

The B650 handset transmitter draws a short burst of current each time it sends a signal to the base. If the Ni-MH pack hasn't completed its first conditioning cycles, internal resistance is elevated and voltage sags under that RF load. The handset interprets the voltage drop as low battery and reduces transmit power, which cuts range. Run three to five full charge-and-use cycles — without putting the handset back in the base mid-cycle — and internal resistance will fall, stabilising transmit voltage above the sag threshold.