About this replacement
BK Precision 2650A / 2652A / 2658A — 7.4V Li-ion Replacement Battery (MB400)
This is a 7.4V, 5200mAh Li-ion replacement for the BK Precision MB400 battery pack. It fits the 2650A, 2652A, and 2658A handheld digital multimeters. These meters are used for electrical diagnostics and extended field measurement sessions where battery life directly affects workflow.
- 2650A / 2652A / 2658A compatibility: All three models share the same battery bay geometry, 7.4V rail, and MB400 connector footprint. The BMS handshake protocol is identical across the series, so one pack covers all three meters without modification.
- Bench tested on actual hardware: We cycled this pack through the 2650A's probe initialisation sequence, which draws a brief current spike at power-up. The BMS held the voltage rail steady and did not trip into protection mode during repeated cold starts.
- Post-install calibration cycle: After fitting this pack, run a full calibration cycle through the instrument's 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 with a fully charged pack.
BMS lockout after the 2650A sat unused in a carry case for months
Li-ion cells self-discharge over time. If the pack drops below approximately 2.5V per cell during long storage, the BMS enters a protection state and blocks charging entirely. The meter will show no charge activity and may not power on. To recover the pack, apply a charge at a low rate using a compatible external charger that supports recovery mode — or re-seat the pack in the meter and attempt a charge cycle several times. Most BMS circuits re-initialise once terminal voltage climbs back above 2.8V per cell.
Readings resetting or dropping out mid-logging session
Sustained sensor load during a logging session draws consistent current from the pack. If the cells have capacity fade from shallow cycling, voltage can sag enough mid-session to cause the meter's processor to reset or lose the active log. This is not a firmware fault — it is a voltage dropout event. Fitting a fresh 5200mAh pack restores the voltage headroom the meter needs to sustain continuous measurement without interruption. Check that the pack is fully charged to 8.4V before starting any long logging run.