About this replacement
Casio Exilim EX-S770SR Series — 3.7V Li-ion Replacement Battery (NP-20)
This is a 3.7V, 650mAh Li-ion cell built to the NP-20 spec. It fits the Casio Exilim EX-S770SR and over 60 other Exilim compact camera bodies that use the same NP-20 footprint. The cell measures 50.80 × 32.45 × 4.60mm — same physical envelope as the original.
- Exilim EX-S770 and EX-S880 platform: Both series share the NP-20 battery slot, the same 3.7V power rail, and the same contact pinout. One cell covers the full range without any modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on an EX-S770 body. The camera's BMS accepted the cell, reported a charge state, and held the LCD on through a full discharge without dropping into low-voltage cutoff prematurely.
- First-cycle calibration on Exilim bodies: Run one complete charge cycle through the camera body or OEM charger before shooting. Exilim cameras map their battery-remaining indicator against a stored voltage curve — skipping this step causes the indicator to read erratically from the first shot.
Dead battery indicator showing on a partially charged NP-20 replacement
Exilim compact cameras use a simple voltage-threshold system to estimate remaining charge. A new third-party cell has a slightly different discharge curve than the original, so the camera can read 3.85V on the cell and still flash the empty battery icon. This is a calibration mismatch, not a faulty cell. Charge the replacement fully in-camera once, let it discharge to auto-off, then charge again — the threshold mapping corrects after one full cycle.
Flash not recycling fully between shots on a new cell
The EX-S770's flash capacitor draws a sharp recharge current spike after each fired shot. If the cell voltage sags below 3.6V mid-shoot — common when the cell is partially discharged or cold — the capacitor recharge slows and the ready indicator lags. This is not a flash fault. Bring the cell to a full charge before a shooting session and keep the camera body above 15°C. At full charge, the cell sustains the capacitor recharge without measurable sag.