Tohnichi CEM10 Replacement Battery HHR-AA 2.4V 2000mAh

TOHNICHI CEM10 / CEM20 / CEM50 Series — 2.4V Ni-MH Replacement Battery (HHR-AA)

This is a 2.4V, 2000mAh Ni-MH replacement battery for the TOHNICHI CEM10, CEM20, CEM50, and 100N3 electronic torque wrench series. It powers the digital measurement display and onboard electronics that handle torque logging and readout. OEM part number HHR-AA.

• CEM and 100N3 series compatibility: These models share the same 2.4V two-cell Ni-MH pack format with the same connector footprint and BMS handshake voltage threshold. The instrument firmware checks cell voltage at startup — a mismatched chemistry or voltage trips an immediate fault flag.
• Bench tested on actual hardware: We cycled this pack through the CEM instrument's measurement and display load profile. The BMS held stable through repeated torque-capture events without triggering voltage dropout or a low-battery interrupt at full display brightness.
• Post-installation calibration step: After fitting this battery, run a full calibration cycle through the instrument menu before field use. The CEM series maps battery state during calibration — skipping this causes the low-battery warning to fire early on the first measurement session, even with a full charge.

BMS lockout after a TOHNICHI CEM pack sat unused in a carry case for months

Ni-MH cells self-discharge at roughly 1–2% per day at room temperature. A CEM unit stored in a case for three or more months can drop cell voltage below the BMS recovery threshold — typically around 0.9V per cell. When the instrument sees voltage this low, it refuses to initialise and shows no response on power-up. Place the pack on a compatible Ni-MH charger for at least 15–20 minutes before attempting to power the instrument; most BMS circuits recover once cell voltage climbs above 1.0V per cell.

Torque reading resets or display blanks mid-logging session

This happens when the cell voltage sags below the instrument's operating floor under sustained display and sensor load — not a dead pack, just a worn one that can't hold voltage under draw. A resting voltage that looks fine at 2.4V can drop to 2.1V or lower the moment the display backlight and torque sensor fire together. The BMS interprets that sag as a cutoff condition and interrupts power to protect the measurement circuit. Replace the pack and confirm resting voltage stays above 2.3V under load before the next calibration session.