Sigma BP-41 DP1 Replacement Battery 3.7V 1150mAh

Sigma DP1 / DP2 Series — 3.7V Li-ion Replacement Battery (BP-41)

This is a 3.7V, 1150mAh Li-ion cell built to the BP-41 specification. It fits the Sigma DP1, DP2, DP1 Merrill, and DP2 Merrill compact digital cameras. Slot it in where the original BP-41 sat and the camera powers on normally.

• DP1 and DP2 Merrill compatibility: All four models share the same BP-41 footprint, connector pinout, and 3.7V voltage rail. The BMS handshake is identical across the standard and Merrill variants, so one cell covers both generations.
• Bench tested on actual hardware: We cycled this cell through the DP1 body and monitored BMS communication at each charge stage. The protection circuit held cutoff at the correct thresholds and the camera's battery indicator tracked discharge without dropping unexpectedly.
• First-charge cycle on the Merrill body: The DP1 Merrill and DP2 Merrill BMS maps battery-remaining percentage against a discharge curve it learns on the first full charge cycle. Run the first charge inside the camera body or OEM charger before a shoot to let that calibration complete accurately.

Battery percentage jumping erratically on the DP1 display

The Sigma DP1 maps its battery indicator to fixed voltage thresholds tied to the original cell's discharge curve. A new BP-41 cell has a slightly different internal resistance profile until it breaks in, so the voltage readings at each threshold don't line up cleanly with what the camera expects. The result is the indicator jumping from three bars to one bar mid-shoot with no warning. Run two full charge and discharge cycles through the camera body and the indicator stabilises as the BMS adjusts its reference points to the new cell.

Camera showing dead battery icon immediately after fitting a charged replacement

This happens when the BP-41 cell resting voltage sits just below the DP1's minimum recognition threshold — typically anything under 3.4V at rest. A cell stored for several months can drop to that level even with remaining capacity. Place the battery in the OEM charger or the camera body on USB charge for 15 minutes to bring it above 3.6V, then reinsert it. The camera will read the charge correctly at that voltage and power on normally.