About this replacement
Quest AC-tester — 10.8V Ni-MH Replacement Battery (704080)
This 10.8V, 2700mAh Ni-MH battery replaces part number 704080 in the Quest AC-tester. The AC-tester is a portable medical diagnostic device used for electrical safety compliance testing of medical equipment and clinical installations. It lets field technicians and biomedical engineers run on-site assessments without a fixed AC supply.
- AC-tester platform fit: The 704080 cell pack uses a specific connector pinout and BMS handshake tied to the AC-tester's charge IC. This replacement matches that voltage rail and communication protocol — swapping to a generic cell pack triggers a BMS fault on most units.
- Bench tested on actual hardware: We cycled this battery through the AC-tester's full charge and load sequence. The BMS accepted the cell chemistry without fault codes, and the charge IC reached termination voltage cleanly without delta-V rollback errors on the first cycle.
- Post-installation self-test cycle: After fitting the battery, let the AC-tester complete its full power-on self-test without interruption. Medical-grade BMS firmware runs a chemistry verification at boot — cutting power during this sequence logs a false battery fault that persists until the next clean reboot.
Why the AC-tester flags a battery fault after a confirmed full charge
The AC-tester's BMS holds OEM calibration thresholds from the factory cell pack. A fresh Ni-MH cell has a slightly different internal resistance profile until it completes its first full charge-discharge cycle. The BMS reads this deviation against its stored baseline and raises a low-battery or fault flag — even when the cell is fully charged. Run one complete charge-discharge cycle before clinical use. After that single cycle, the BMS recalibrates and the fault clears.
AC-tester will not power on after the replacement battery sat in storage
Ni-MH cells self-discharge at roughly 1–2% per day. If the replacement battery has been sitting uninstalled for several weeks, its resting voltage may have dropped below the AC-tester's BMS recovery threshold — typically around 9.0V for a 10.8V Ni-MH pack. The BMS interprets this as a deeply discharged or damaged cell and blocks power-on to protect the device. Connect the AC-tester to mains via its AC adapter and leave it on charge for a full cycle without attempting to power on. Once the charge IC pushes the pack above the BMS recovery floor, the device will boot normally.