Panasonic DMW-BLJ31 Lumix S1 Replacement Battery 7.4V 3400mAh

Panasonic Lumix S1 / S1R — 7.4V Li-ion Replacement Battery (DMW-BLJ31)

This is a 7.4V, 3400mAh Li-ion replacement for the Panasonic DMW-BLJ31 and DMW-BLJ31E batteries. It fits the Lumix S1 and S1R full-frame mirrorless cameras. Use it for stills, video, or any extended shooting session where the original cell is depleted or unavailable.

• Lumix S1 and S1R fit: Both cameras run the same 7.4V battery rail, share the same grip connector pinout, and use identical BMS handshake protocols — one cell covers both bodies without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on an S1 body. The BMS accepted the cell after one full charge via the camera body, reported capacity correctly, and held voltage stable through sustained 4K recording loads.
• First-cycle initialisation on the S1: Insert the new cell and run one complete charge cycle through the camera body or OEM charger before heavy use. The S1's BMS maps its battery-remaining display to the cell's discharge curve — skipping this step can cause the indicator to read inaccurately for the first several cycles.

Why the S1's battery drain accelerates under sustained 4K video

The Lumix S1 pulls current from three major loads simultaneously during 4K recording: the full-frame sensor readout, the Venus Engine processor, and the in-body 5-axis image stabilisation system. Combined draw is significantly higher than during still shooting. A cell that reads 60% during photo use can drop to cutoff much faster once video starts. Monitoring the battery indicator actively during long video sessions is the only reliable way to avoid unexpected shutdowns mid-clip.

Battery percentage jumping erratically on the S1 display

This happens when the camera's BMS is still mapping a new cell's discharge curve to its indicator thresholds. The S1 uses voltage-based percentage reporting, and a fresh cell's voltage curve sits slightly differently than a used OEM cell the camera previously learned. The fix is straightforward: run two or three full charge-discharge cycles through the camera body. By the third cycle, the indicator stabilises and tracks accurately against the cell's actual state of charge.