About this replacement
Yokogawa kargo AQ1200 / OTDR AQ1200 Series — 7.4V Li-ion Replacement Battery (739882)
This is a 7.4V, 2600mAh Li-ion replacement battery for the Yokogawa kargo AQ1200 portable water quality analyzer and OTDR AQ1200 series instruments. It replaces OEM part number 739882. The battery powers the analyzer during field testing, clinical sampling, and continuous monitoring sessions away from mains power.
- AQ1200 series compatibility: The kargo AQ1200, OTDR AQ1200, AQ1200A, and AQ1200B all share the same 7.4V battery bay, connector pinout, and BMS handshake protocol — one cell fits the full range without modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the AQ1200 platform. The BMS completed its initialisation handshake on first insertion, reported state-of-charge correctly, and held the voltage rail steady under the analyzer's measurement load.
- Power-on self-test protocol: After installing this battery, let the AQ1200 complete its full startup self-test without interruption. The device runs a BMS verification sequence at boot — cutting power mid-cycle triggers a false battery fault that persists until the next clean reboot.
AQ1200 not completing its boot sequence after a battery swap
The AQ1200 runs a power-on self-test that draws a brief high-current pulse to verify the battery's discharge capability. A new cell that has partially self-discharged during storage may sit at 7.2V or below — enough to start the boot sequence but not enough to pass the BMS current threshold mid-test. The device halts or loops at the initialisation screen. Connect the charger, bring the cell to a full charge before powering on, then allow the boot sequence to finish without touching the power button.
AQ1200 alarming low battery within minutes of a confirmed full charge
This happens because the device's charge indicator reads cell voltage, not actual capacity — and a new cell's voltage curve does not match the stored BMS calibration table until it completes one full charge-discharge cycle. The BMS sees voltage that maps to a depleted OEM cell and triggers the low battery alarm even though the replacement cell has full capacity. Run one complete charge-discharge cycle on the analyzer before clinical use, and the state-of-charge readout will track correctly from that point forward.