Phase One 645DF Compatible Battery 7.4V 2000mAh UA002418

PHASEONE 645DF / 645AF Series — 7.4V Li-ion Replacement Battery (UA002418)

This 7.4V 2000mAh (14.8Wh) lithium-ion cell replaces the OEM UA002418 battery in Phase One medium format camera systems. It fits the 645DF, 645DF+, 645AF, and 645AFII bodies. Voltage and capacity match OEM spec exactly — no modification needed.

• 645DF, 645DF+, 645AF, and 645AFII compatibility: All four bodies share the same battery bay geometry, contact pin layout, and 7.4V power rail. The BMS handshake protocol is consistent across the series, so one cell works across all four platforms without firmware differences affecting recognition.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a 645-series body. The BMS accepted the cell without fault codes, held voltage within spec across the full discharge curve, and triggered the low-battery cutoff at the correct threshold.
• First-use charge cycle on medium format bodies: Charge this cell fully inside the camera body or OEM charger before your first shoot. Phase One's BMS uses an internal calibration pass during the first charge cycle to map the cell's discharge curve to the battery-remaining indicator — skipping this step causes erratic percentage readings.

Why the 645DF battery percentage jumps erratically after fitting a new cell

The 645DF reads remaining charge by mapping voltage at rest against a stored discharge curve from the previous cell. A new cell has a slightly different voltage-versus-capacity profile, so the camera's fuel gauge misreads position on that curve. This shows up as the percentage jumping from 80% to 40% mid-session with no actual power loss. Running one full charge-to-full, discharge-to-cutoff cycle through the camera body lets the BMS remap to the new cell. After that cycle, percentage display stabilises.

Camera displaying dead-battery icon immediately on a charged replacement cell

This happens when the BMS has not yet authenticated the new cell — it defaults to a dead-battery state rather than risking a mid-shoot shutdown. The fix is not to recharge the cell externally; the body needs to initiate the charge itself. Seat the cell, connect the body to the OEM charger, and let it run a full charge cycle from inside the camera. Once the body completes that cycle, it clears the authentication flag and reads voltage correctly. At that point the indicator should show full charge at approximately 8.4V.