About this replacement
Sony Cyber-shot DSC-T20/B Series — 3.7V Li-ion Replacement Battery (NP-BG1)
This is a 3.7V, 1000mAh Li-ion replacement for the Sony NP-BG1 and NP-FG1 battery. It fits the Cyber-shot DSC-T20/B and over 130 other Cyber-shot compact cameras including the DSC-W215, DSC-W40, and DSC-W55. Dimensions are 41.90 × 35.40 × 8.10mm — same form factor as the OEM cell.
- Cyber-shot G-type slot compatibility: Sony's NP-BG1 and NP-FG1 share the same physical connector and voltage rail. The BMS on these Cyber-shot bodies uses a single-wire handshake over the centre pin. Both part numbers clear that handshake on the DSC-T20/B, W215, and W40 platforms.
- Bench tested on actual hardware: We ran this cell through the DSC-T20/B body. The BMS accepted the cell on first install, charge termination triggered correctly at 4.2V, and the camera's battery indicator mapped consistently across the full discharge cycle.
- First charge cycle on the T20/B: Charge this battery from inside the camera body using Sony's OEM charger or the body's USB port before your first shoot. The DSC-T20/B calibrates its battery-remaining display from the charge profile it reads during that first cycle — skipping this step causes the indicator to read incorrectly.
Flash capacitor recharge sag at the end of the cell's discharge curve
The DSC-T20/B's flash capacitor draws a sharp current spike to recharge between shots. Near the bottom of the battery's discharge curve — below roughly 3.5V — the cell's internal resistance rises enough that this spike causes a brief voltage sag. The camera body reads that sag as a low-battery condition and may cut the flash or shut down before the indicated charge reaches zero. This is normal cell behaviour, not a fault in the replacement battery.
Battery percentage jumping erratically after inserting a new cell
A new cell has a discharge curve that doesn't yet match the voltage-threshold map stored in the camera's fuel gauge logic. The T20/B reads voltage at rest and estimates percentage from a fixed lookup table — a fresh cell at partial charge can sit at a voltage that maps to a different percentage than expected. Complete one full charge-to-discharge cycle in the camera body. After that cycle, the indicator tracks the new cell's curve accurately and the jumping stops.