BK Precision MB400 7.4V Replacement Battery 2650A Multimeter

BK Precision 2650A / 2652A / 2658A — 7.4V Li-ion Replacement Battery (MB400)

This is a 7.4V 6800mAh Li-ion battery for the BK Precision 2650A, 2652A, and 2658A handheld digital multimeters. It replaces OEM part MB400. These multimeters are portable test instruments used by field technicians for voltage checks, circuit diagnostics, and equipment fault-finding.

• 2650A / 2652A / 2658A compatibility: All three models share the same battery bay dimensions, MB400 part number, and 7.4V power rail. The BMS handshake protocol is identical across the series, so one pack covers all three without modification.
• Bench tested on actual hardware: We ran this pack through power-on sequencing and probe initialisation cycles on the 2650A. The BMS handled the short current spike at probe activation without tripping, and the instrument accepted the pack without throwing a battery fault code.
• Post-install calibration cycle: After fitting this battery, run a full calibration cycle through the instrument menu before field deployment. The 2650A maps battery state during calibration — skipping this step causes premature low-battery warnings during your first measurement session, even when the pack is well charged.

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

Li-ion cells self-discharge slowly in storage. If a 2650A sits unused long enough, the pack voltage drops below the BMS recovery threshold — typically around 2.5V per cell, or roughly 5.0V combined for a 2S pack. At that point, the BMS enters a protective lockout state and the instrument will not power on, even when placed on charge. A slow pre-charge at low current is required to bring cell voltage back above the recovery threshold before normal charging resumes. Use a charger capable of trickle or recovery mode, and expect the pack to sit at the initiation stage for up to 30 minutes before the BMS re-enables the charge circuit.

Readings drifting or logging session resetting mid-test

When the 2650A runs sustained sensor load — continuous data logging, backlight on, active probe supply — total current draw rises sharply compared to spot-check use. An aged or partially depleted cell can hold a resting voltage that looks acceptable but sags below the instrument's operating threshold under that combined load. The 2650A interprets the voltage dropout as a power fault and resets the active logging session. If this happens, check resting pack voltage with a DMM — a healthy 7.4V Li-ion pack at partial charge should read above 7.0V at rest. Below that under load, the pack needs replacement.