Pentax D-Li78 Optio M50 Replacement Battery 3.7V 680mAh

Pentax Optio M50 / M60 / W60 Series — 3.7V Li-ion Replacement Battery (D-Li78)

This is a 3.7V 680mAh Li-ion cell built to the D-Li78 spec. It fits the Pentax Optio M50, M60, V20, and W60, along with seven additional Optio models that share the same battery form factor and voltage rail. The physical dimensions are 38.20 × 26.82 × 7.34mm — same footprint as the OEM cell.

• Optio series shared battery platform: These models use the same compact Li-ion cell because they share an identical battery bay, contact layout, and 3.7V power rail. No adapters or wiring changes are needed — the cell seats and connects the same way as the original.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a D-Li78-compatible body. The BMS accepted the cell without error flags, held voltage within the expected discharge curve, and cut off cleanly at the low-voltage threshold.
• First-cycle initialisation on Optio bodies: Insert the new cell and run a full charge cycle through the camera body before your first shoot. Some Optio firmware maps the battery-remaining indicator to the charge cycle history — skipping this step can cause the indicator to read inaccurately from the start.

Why the Optio W60 battery indicator drops sharply at full charge

The W60 and other Optio bodies use a voltage-threshold method to estimate remaining charge rather than a fuel gauge IC. A new cell's discharge curve can sit slightly outside the voltage windows the firmware expects, especially in the upper charge range. This makes the indicator jump from full to mid-level within the first few shots. After one or two complete charge-discharge cycles, the cell's resting voltage stabilises and the display tracks more accurately. No fault in the cell — it's the firmware mapping to an unfamiliar curve.

Flash not fully recycling between shots on the new cell

The built-in flash on Optio compacts draws a short, high-current burst to recharge the capacitor between shots. Near the end of a cell's charge, voltage sag under that load slows the recharge cycle. If the flash warning light stays on longer than usual between shots, the cell is below roughly 3.5V under load — not a fault, but a sign the cell needs charging. Charge the battery fully and the recycle time returns to normal.