AMC 3945 Replacement Battery 9.6V 3600mAh Ni-MH 2140.19

AMC 3945/3945-B Series — 9.6V Ni-MH Replacement Battery (2140.19)

This is a 9.6V, 3600mAh Ni-MH replacement battery for AMC surveying and measurement instruments. It fits the 3945, 3945-B, 8333, 8335, and 8336 models, along with five additional compatible units in the same instrument family. Voltage and connector match the original pack exactly.

• 3945/3945-B and 8333–8336 series fit: These models share the same 9.6V eight-cell Ni-MH voltage rail, identical connector pinout, and the same current threshold in the instrument's power management circuit. One pack covers the full group without modification.
• Bench tested on actual hardware: We cycled this pack through three charge-discharge sequences and monitored BMS handshake at probe initialisation. The cell stack held voltage above the instrument's low-battery cutoff through sustained sensor load without triggering a spurious shutdown.
• Instrument calibration cycle before first field use: After installing this pack, run a full calibration cycle through the instrument menu before taking it to site. The 3945 series maps battery state during calibration — skipping this step causes premature low-battery warnings on your first measurement session, even with a fully charged pack.

BMS cutoff at probe or sensor initialisation on the 3945 series

When the 3945 powers up a probe module, it draws a short current spike as the sensor circuit initialises. A degraded or partially discharged Ni-MH pack can drop below the BMS cutoff threshold during that spike, causing the instrument to shut off immediately after probe connection. This is not a faulty instrument — it's a cell voltage sag event. A fully charged pack with healthy cells clears the initialisation spike without tripping the cutoff.

Readings drifting or logging session resetting mid-measurement

Under sustained sensor load during a logging session, an ageing pack develops a voltage dropout that falls below the 3945's operating floor. The instrument interprets this as a low-power event and resets the active session to protect data integrity. The fix is not a restart — it's a full charge before the session and a check that resting voltage reads at or above 10.8V after charging. If the pack won't hold above that threshold, the cells have fatigued beyond recovery and need replacing.