About this replacement
Sony CX405 Handycam & DSC-HX Series — 3.7V Li-ion Replacement Battery (NP-BX1)
This is a 3.7V, 1150mAh Li-ion replacement cell for the NP-BX1 battery slot. It fits the Sony CX405 Handycam, DSC-HX90V, DSC-HX99, and over 100 additional Sony camera and camcorder bodies that share the NP-BX1 form factor. Voltage, capacity, and physical dimensions match OEM spec — 42.70 × 29.70 × 9.10mm.
- NP-BX1 platform compatibility: Sony standardised the NP-BX1 slot across compact cameras, camcorders, and action cams using the same 3.7V rail and the same physical locking tab. Any body with an NP-BX1 door will accept this cell — the BMS handshake uses the same communication protocol across the entire lineup.
- Bench tested on actual hardware: We ran this cell through the Sony charge-discharge cycle on a CX405 body. The BMS accepted the cell on the first charge, reported state-of-charge accurately at 25°C, and hit 1150mAh within normal tolerance across three full cycles.
- First-use charge cycle on NP-BX1 bodies: Charge this cell fully inside the camera body or OEM charger before shooting. Some Sony BMS firmware maps the battery-remaining display to a discharge curve it only calibrates after one full in-camera charge cycle — skipping this step causes the indicator to read inaccurately from the start.
Sony BMS authentication rejecting a new NP-BX1 cell on first install
Some Sony bodies — especially DSC-HX and CX-series camcorders — display a battery warning or refuse to power on when a new third-party cell is inserted cold. This is a BMS authentication check, not a cell defect. The body expects to see a voltage handshake within a narrow window on first contact. Insert the cell, place the body on charge via the OEM BC-TRX charger or the USB port, and let it complete one full charge cycle. That single charge pass typically resolves the rejection on the first attempt.
Battery percentage jumping erratically on the CX405 display
If the remaining-charge indicator skips — say, from 80% to 40% without warning — the Sony BMS is mapping a new cell's discharge curve against the lookup table it built for the worn original. A new lithium cell has a flatter discharge curve than a degraded one, so the threshold crossings hit at unexpected points. Run two full charge-discharge cycles through the camera body to let the BMS recalibrate its curve mapping. After those cycles, the indicator should track the actual cell voltage consistently down to the 3.0V cutoff.