About this replacement
Sony NEX-5 / NEX-5A / NEX-5K / NEX-5D Series — 7.4V Li-ion Replacement Battery (NP-FW50)
This is a 7.4V, 1050mAh Li-ion replacement cell for the Sony NP-FW50 battery pack. It fits the NEX-5, NEX-5A, NEX-5K, and NEX-5D mirrorless camera bodies, along with over 90 additional Sony Alpha and NEX models that share the same NP-FW50 form factor. Voltage and capacity match the OEM spec exactly.
- NEX-5 series compatibility: The NEX-5, NEX-5A, NEX-5K, and NEX-5D all run on the same 7.4V battery rail and use identical connector orientation and BMS communication protocol — which is why one NP-FW50 cell covers the entire line.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a NEX-5 body. The BMS handshake completed correctly, the camera's battery icon populated without error flags, and the protection circuit triggered at the expected low-voltage cutoff point.
- First-install charge cycle: Before your first shoot, run one full charge inside the camera body or OEM charger rather than a third-party charger. Sony's BMS maps its battery-remaining display to the cell's discharge curve during that initial cycle — skipping it can cause the percentage indicator to read inaccurately from the start.
Sony BMS rejecting a third-party NP-FW50 cell on first install
Sony camera bodies run an authentication check when a new cell is inserted. If the BMS doesn't receive the expected response during that first handshake, it can flag the battery as unrecognised even when the cell voltage is correct. This most often happens when the cell is inserted into the body cold and without a prior charge. Placing the battery in the OEM charger first — until the charge indicator shows full — then inserting it into the camera body typically clears the rejection flag. If the error persists after one full OEM charge cycle, try a power cycle: remove the battery, wait 10 seconds, and reinsert.
Battery percentage jumping erratically on the NEX-5 display
This happens when the camera's fuel gauge hasn't yet mapped its voltage-threshold table to the new cell's discharge curve. The OEM firmware calibrates the indicator against a reference discharge profile — a new third-party cell with a slightly different internal resistance can cause the percentage to jump or drop suddenly at certain voltage steps. The fix is to run two full charge-to-depletion cycles through the camera body, not a standalone charger, so the BMS can observe the actual discharge curve of this specific cell. After those two cycles, the indicator typically stabilises and tracks accurately down to the 3.0V per-cell cutoff.