About this replacement
Kyocera CONTAX SL300RT — 3.7V Li-ion Replacement Battery (BP-780S)
The BP-780S is a 3.7V, 700mAh Li-ion cell that powers the CONTAX SL300RT, Finecam SL300R, and Finecam SL400R digital cameras. It drives the autofocus, exposure metering, and LCD functions that make the camera operational. Capacity figure is taken directly from product specifications at 2.59Wh.
- SL300RT / Finecam SL300R / Finecam SL400R platform: These three cameras share the same battery bay geometry, connector pinout, and 3.7V supply rail — the BP-780S fits each body without modification or adapter.
- Bench tested on actual hardware: We ran this cell through a charge and discharge cycle monitoring the BMS communication. The protection circuit responded correctly to over-discharge cutoff and resumed charging without fault flags when reconnected to the charger.
- First-cycle conditioning for accurate metering: The SL300RT's battery-level indicator maps voltage thresholds from the first charge cycle it sees a new cell complete inside the camera body. Charge the replacement fully via the OEM charger or camera body before heavy use — otherwise the indicator may read low even when the cell is not depleted.
Why the SL300RT shows a dead battery icon on a freshly charged replacement
The SL300RT reads remaining charge by comparing the cell's voltage curve against a stored reference profile. A new cell with no charge history inside that specific body can produce a mismatch between its actual voltage and what the camera expects at that state of charge. The camera interprets the unfamiliar curve as a low or exhausted cell and triggers the indicator early. One complete charge cycle performed inside the camera body or OEM cradle resets that reference and allows accurate display from that point forward.
Battery percentage jumping erratically mid-shoot
This happens when the camera's voltage-threshold map doesn't align with the discharge curve of the new cell. The indicator jumps because the camera is sampling voltage at points where the new cell's curve drops more steeply or shallowly than the original. It is a display calibration issue, not a fault with the cell itself. Fully discharge and then fully recharge the battery once inside the camera — after that cycle, the indicator should track the remaining charge without erratic jumps, stabilising around 3.7V nominal mid-charge.