About this replacement
Ando AQ7250 / AQ7250 Mini-OTDR — 10.8V Ni-MH Replacement Battery (9HR-4/3FAU)
This is a 10.8V, 3500mAh Ni-MH replacement battery for the Ando AQ7250 and AQ7250 Mini-OTDR optical time-domain reflectometers. It replaces OEM part number 9HR-4/3FAU. Both instruments run on the same battery platform and connector configuration.
- AQ7250 and AQ7250 Mini-OTDR compatibility: Both units share the same 10.8V battery rail, connector pinout, and BMS handshake protocol — one pack covers either instrument without modification.
- Bench tested on actual hardware: We ran this pack through the AQ7250 power-on sequence and monitored BMS response during optical probe initialisation. The cell array held voltage through the laser-module startup spike without triggering a protection cutoff.
- Post-install calibration step: After fitting this pack, run a full instrument calibration cycle through the AQ7250 menu before field deployment. The instrument maps battery state during calibration — skipping this causes premature low-battery warnings to appear during your first measurement session.
BMS cutoff during laser module initialisation on the AQ7250
When the AQ7250 powers up, the laser and optical probe draw a short, sharp current spike before settling into steady-state measurement load. A degraded or deeply discharged Ni-MH pack can drop below the BMS undervoltage threshold during that spike, triggering an immediate protection cutoff that looks like a dead battery. This is a cell-state issue, not a fault in the instrument. Charge the pack fully — confirmed at the charger's green light — then power on the instrument while the pack is still warm from charging, which reduces internal resistance and softens the voltage sag on that first spike.
AQ7250 displaying a frozen or jumping battery percentage at reboot
The AQ7250 estimates charge state from a voltage threshold map calibrated to the original cells. A new or replacement Ni-MH pack has a different resting voltage profile until it has been through several charge-discharge cycles, so the percentage indicator recalibrates slowly and can read 40% one boot and 75% the next. This is normal for the first three to five full cycles. Run the instrument until the low-battery warning appears, then charge to completion — repeating this three times stabilises the reading. After conditioning, the display should track consistently within a few percentage points of actual remaining charge.