Doro 401 DBC-800A Replacement Battery 3.7V 900mAh

Doro 401 / 507S / 508 / 509 Series — 3.7V Li-ion Replacement Battery (DBC-800A)

This is a 3.7V, 900mAh Li-ion cell built to fit the Doro 401, 507S, 508, 509, and over 46 additional Doro handsets that share the DBC-800A footprint. The physical dimensions are 53.00 × 34.00 × 4.30mm — measure your original before ordering if you are unsure. Capacity is 900mAh (3.33Wh), matching the OEM spec.

• Cross-model fit — 401, 507S, 508, 509 and more: These handsets share the same battery bay dimensions, 3.7V voltage rail, and connector pinout. Doro standardised this cell across multiple budget and accessibility-focused handsets, so one part number — DBC-800A — covers the full range.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the bench, confirmed BMS communication with the charge IC, and verified the protection circuit trips correctly at low-voltage cutoff. No anomalies in charge acceptance or cutoff behaviour were observed.
• Fuel gauge recalibration after swap: On first use after fitting this cell, run one complete discharge down to auto-shutdown, then charge uninterrupted to 100%. This gives the fuel gauge IC one full cycle to map the new cell's discharge curve before the OS starts reading percentage from it.

Why the Doro 401 reports wrong battery percentage after a cell swap

The fuel gauge IC on this handset uses a coulomb counter that was calibrated to the original cell's discharge curve. When a new cell goes in, that stored curve no longer matches actual cell behaviour, so the percentage reading drifts. The phone may show 40% and shut down, or sit at 100% longer than expected. One full discharge-to-shutdown followed by an uninterrupted charge to 100% resets the calibration. After that cycle, percentage accuracy stabilises.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff problem, not a capacity problem. Under modem transmission load or a bright screen, the cell voltage drops sharply — and if it hits the BMS cutoff threshold before the fuel gauge expected it to, the phone shuts off hard. It typically happens because the fuel gauge is still running the old cell's curve and underestimates how close the new cell is to cutoff. Complete the recalibration cycle described above. If shutdowns persist after two full cycles, check that the battery contacts are seated flat — a loose connection increases resistance and accelerates the voltage sag under load.