BK Precision BP2650 4.8V Replacement Battery 4500mAh Ni-MH

BK Precision 2650 Series — 4.8V Ni-MH Replacement Battery (BP2650)

This is a 4.8V, 4500mAh Ni-MH battery built to replace the original BP2650 pack. It fits the BK Precision 2650, 2652, 2658, and Spectrum Analyzer models. All four share the same voltage rail, connector, and BMS handshake, so one part number covers the group.

• 2650, 2652, 2658, and Spectrum Analyzer compatibility: These models run on the same 4.8V four-cell Ni-MH architecture with a common connector and identical BMS communication protocol. Swapping packs between them works because the charge termination logic is shared across the platform.
• Bench tested on actual hardware: We cycled this pack through the 2650's charge and measurement modes. The BMS accepted the new cells without error flags, and voltage held steady under sustained probe load across multiple measurement sessions.
• Post-install calibration cycle: After fitting this pack, run a full calibration cycle through the instrument menu before field deployment. The 2650 maps battery state during calibration — skipping this step causes premature low-battery warnings on the first measurement session, even with a full charge.

BMS lockout after the 2650 sat unused in a carry case for months

Ni-MH cells self-discharge over storage, and the 2650's BMS enters a protective sleep state when pack voltage drops below a recovery threshold. In this state, the instrument will not power on and may not respond to a standard charger. The fix is to apply a slow trickle charge — most Ni-MH smart chargers have a recovery or recondition mode that pushes a low current to wake the cells. Once voltage climbs above approximately 4.2V, the BMS exits sleep and normal charging resumes.

Readings resetting or dropping out mid-logging session

This happens when sustained sensor load pulls pack voltage below the instrument's operating floor, triggering a brief reset rather than a clean shutdown. It is not a faulty battery — it is a voltage sag event under continuous draw. A degraded or partially charged pack cannot hold the rail steady when the 2650 is logging at high sample rates. Charge the pack fully before a long logging session and verify resting voltage reads at or above 5.4V before starting.