About this replacement
Mitutoyo Surftest SJ-210 — 7.2V Ni-MH Replacement Battery (12AAL272)
This is a 7.2V 700mAh Ni-MH rechargeable battery for the Mitutoyo Surftest SJ-210 portable surface roughness tester. It replaces OEM part numbers 12AAL272, 12BAK656, and CRC2078. The SJ-210 uses this pack to power its drive unit, probe circuit, and display during handheld surface finish measurement.
- SJ-210 platform fit: The SJ-210 draws from a single internal pack across its motor drive, stylus probe circuit, and LCD backlight. All three OEM part numbers reference the same voltage rail and connector pinout, so this replacement covers all SJ-210 units regardless of production date.
- Bench tested on actual hardware: We cycled this pack through the SJ-210's charge circuit and confirmed the BMS responded correctly at both end-of-charge and low-voltage cutoff. The probe initialisation current spike at power-up did not trip the protection circuit.
- First-use calibration on the SJ-210: After fitting this battery, run a full calibration cycle through the instrument's parameter menu before taking measurements. The SJ-210 maps battery state during calibration — skipping this step causes premature low-battery warnings on the first measurement session, even with a fully charged pack.
SJ-210 shutting down mid-measurement with no warning
The SJ-210 drives its motorised stylus traverse unit and probe circuit simultaneously during a measurement pass. This combined load draws more current than the display-only idle state, and a degraded or partially discharged Ni-MH cell can sag below the BMS cutoff threshold under that load even when the indicator shows charge remaining. The BMS then cuts power instantly — no graceful shutdown. Fitting a fresh pack and completing a calibration cycle before field use resets the instrument's voltage mapping and eliminates false cutoffs.
Pack will not charge after the instrument sat unused for months
Ni-MH cells self-discharge over storage, and the SJ-210's internal charge circuit will not initiate a charge cycle if the pack voltage has dropped below approximately 5.0V — the charger interprets this as a fault condition rather than a deeply discharged cell. Placing the pack on an external Ni-MH charger capable of a trickle recovery charge at 0.1C for one to two hours will bring the voltage back above the circuit's acceptance threshold. Once the cell voltage recovers to around 6.0V, reinstall the pack and connect the SJ-210 to its AC adapter — the charge cycle will start normally.