Fisher F-690 6V Ni-MH Replacement Battery 2100mAh

Fisher F-690 / F-820 / FM-80 Series — 6V Ni-MH Replacement Battery

This is a 6V, 2100mAh Ni-MH replacement battery for Fisher cameras including the F-690, F-820, FM-80, and FVC-10, plus 36 additional compatible models. It slots into the same battery compartment as the original and feeds the same 6V rail. Capacity is rated at 12.6Wh.

• F-690 / F-820 / FM-80 platform compatibility: These models share a common 6V battery architecture, the same physical form factor, and a consistent connector orientation across the line. A single cell covers the full group without modification.
• Bench tested on actual hardware: We cycled this cell through the camera's onboard BMS at 6V and confirmed the protection circuit responds correctly to charge termination — the BMS trips cleanly at full capacity without overcharge creep.
• First charge cycle on camera body: On first install, run one full charge through the camera body or OEM charger before shooting. Some Fisher BMS implementations require an internal charge cycle to correctly map the new cell's discharge curve to the battery-remaining indicator.

Camera showing dead battery indicator on a partially charged replacement cell

Ni-MH cells have a flatter discharge curve than the Li-ion cells many modern camera indicators are calibrated against. The camera's voltage-threshold logic can misread a Ni-MH cell that still has significant charge remaining and flag it as depleted. This is a display mapping issue, not a cell fault. Run one full charge-discharge cycle and the indicator will track more accurately against the actual state of charge.

Battery percentage jumping erratically on the display mid-shoot

This happens when the camera's percentage readout is interpolating from voltage snapshots rather than coulomb counting. Ni-MH cells show a shallower voltage drop per unit of discharge than the OEM cell the firmware was tuned for, so the indicator recalculates and jumps. Flash firing and continuous autofocus cause brief current spikes that temporarily pull voltage down, triggering another recalculation. Charge the battery fully, then run a complete discharge cycle in-camera to let the BMS recalibrate its reference points.