Acutrac NB-1X7 Survey Battery 8.4V 700mAh Ni-MH

Acutrac 22 Pro / Digisat Pro Series — 8.4V Ni-MH Replacement Battery (NB-1X7)

This is an 8.4V 700mAh Ni-MH replacement battery for the Acutrac 22 Pro surveying instrument. It also fits the Digisat Pro, Digiair, and MKII satellite signal meter. Voltage and connector match the original NB-1X7 specification exactly.

• 22 Pro and Digisat Pro platform fit: These models share the same 8.4V power rail and NB-1X7 footprint. The connector orientation, cell count, and BMS handshake requirements are identical across the family, so one battery covers all listed variants without modification.
• Bench tested on actual hardware: We ran this pack through charge and discharge cycles on the 22 Pro. The BMS accepted the charge profile without fault flags, and the instrument's power management circuit read cell state correctly throughout each cycle.
• Field calibration before first deployment: After installing this battery, run a full calibration cycle through the instrument menu before heading into the field. The 22 Pro maps battery state during calibration — skipping this step causes premature low-battery warnings on the first measurement session, even with a fully charged pack.

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

Ni-MH cells self-discharge at roughly 1–2% per day at room temperature. A pack left unused for several months can drop below the BMS recovery threshold — typically around 6.0V for an 8.4V Ni-MH pack — causing the protection circuit to latch open. When this happens, the instrument shows no sign of life even after placing it on charge. The fix is a slow trickle charge at low current (around 50mA) directly across the cell terminals using a bench charger until the pack reaches 7.0V, at which point the BMS will re-initialise and accept a normal charge cycle.

Readings drifting or resetting mid-session during continuous logging

During sustained sensor load — continuous GPS or signal logging with backlight active — current draw climbs steadily and can cause brief voltage dropouts across the pack. The 22 Pro's processor interprets these dropouts as a low-voltage event and either resets or interrupts the active logging session. This is not a faulty battery; it is a cell-voltage sag issue common to Ni-MH chemistry under sustained draw. To reduce dropout risk, dim the backlight and close unused instrument functions during long logging sessions, keeping continuous draw below the threshold where cell voltage sags past 7.2V under load.