Rollei DS-SD20 Bullet 3S Compatible Battery 3.7V 900mAh

Rollei Bullet 3S / 4S / 5S — 3.7V Li-Polymer Replacement Battery (DS-SD20)

The DS-SD20 is a 3.7V 900mAh lithium-polymer cell for the Rollei Bullet action camera series. It fits the Bullet 3S, Bullet 4S, Bullet 5S, and the WiFe Hama Star, along with seven additional compatible models. At 3.33Wh, it matches the OEM energy spec in the same compact 37.84 × 31.71 × 11.36mm form factor.

• Bullet 3S / 4S / 5S platform compatibility: These cameras share the same battery bay dimensions, 3.7V nominal rail, and connector pinout. The DS-SD20 part number covers all three variants because the BMS voltage thresholds and charge termination logic are identical across the Bullet series.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Bullet platform and confirmed the BMS accepted the cell without rejection flags. Charge termination triggered correctly at 4.2V, and low-voltage cutoff engaged at the expected floor.
• First-use charge cycle in-camera: Insert the new cell and charge it once through the camera body or OEM charger before shooting. Some Bullet BMS versions need one full in-camera charge cycle to map the cell's discharge curve — skipping this can cause the battery indicator to read inaccurately from the first session.

Why the Bullet series shows a dead-battery icon on a partially charged replacement cell

The Bullet camera maps its battery indicator against a stored voltage-to-capacity curve from the previous cell. A new lithium-polymer cell has a slightly different open-circuit voltage profile at each state of charge. Until the camera re-calibrates that curve, it can misread a cell sitting at 3.9V as nearly flat. Running one complete charge-discharge cycle through the camera body resets the reference points the indicator uses. After that cycle, the display tracks remaining charge accurately.

Battery percentage jumping erratically during recording or playback

Continuous video recording pulls sustained current from the cell — sensor, processor, and video encoder all draw simultaneously. When the camera samples voltage under that combined load, the reading dips; when load briefly drops, voltage recovers and the display jumps up. This is a voltage-sag artefact, not a fault in the cell. If the jumps are severe, check that the cell contacts are clean and seated flush — even a slight gap increases contact resistance and amplifies the sag. A fully topped cell at 4.2V will show the most stable readings at the start of a recording session.