Metz 9637 Flash Replacement Battery 6V 2100mAh Ni-MH

Metz 9637 / 9702 / 9704 / 9705 Series — 6V Ni-MH Replacement Battery

This is a 6V 2100mAh Ni-MH replacement battery for Metz flash units including the 9637, 9702, 9704, and 9705, plus twelve additional models in the same series. It powers the flash's charging capacitors and control circuitry. Without a functional cell at the correct voltage, the flash cannot cycle or fire.

• Metz 9637 / 9702 / 9704 / 9705 compatibility: These flash units share the same battery bay geometry, connector orientation, and 6V supply rail. The BMS in each model accepts cells within the same voltage window, so one replacement cell covers all listed units without modification.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge sequences on Metz flash hardware. The BMS accepted the cell without rejection flags, and capacitor recharge current remained stable across repeated firing cycles at full power.
• First-cycle conditioning on Metz flash units: Ni-MH cells in Metz flashes benefit from one complete charge cycle using the OEM Metz charger before heavy use. Skipping this step can cause the flash's charge-ready indicator to trigger early, giving a false ready signal before the capacitor has fully charged to firing voltage.

Capacitor recharge current sag on a new Ni-MH cell

A new Ni-MH cell at partial capacity delivers lower peak current than a fully conditioned one. In Metz flash units, the capacitor recharge circuit draws a sharp current spike immediately after each firing. If the cell hasn't completed at least one full charge cycle, internal resistance is slightly elevated and that spike can cause a voltage dip. The flash interprets this dip as a low-battery state and slows the recharge cycle. One full charge from a depleted state resolves it.

Flash ready light coming on before full capacitor charge

The ready indicator on Metz flash units monitors voltage recovery after a firing event, not the actual energy stored in the capacitor. A new or recently replaced Ni-MH cell with slightly different discharge curve characteristics can recover voltage quickly while the capacitor is still partially charged. This causes the ready light to trigger at 70–80% capacitor charge rather than full. Fire the flash at full power and measure guide number output — if it falls short of the rated value, the cell needs further conditioning cycles before the BMS calibrates to its discharge curve correctly.