Doro Primo 406 Replacement Battery RCB01P01 3.7V 1200mAh

Doro Primo 406 / 413 / 414 — 3.7V Li-ion Replacement Battery (RCB01P01)

This is a 3.7V, 1200mAh Li-ion cell for the Doro Primo 406, Primo 413, and Primo 414 — basic mobile phones built for senior users. The OEM part numbers RCB01P01, RCB413, and RCBNTC01 all cross to this cell. Physical dimensions are 53.45 × 36.88 × 5.75mm — measure your original before fitting.

• Primo 406, 413, and 414 compatibility: All three models share the same battery bay dimensions, connector pinout, and NTC thermistor line. The charge IC on each handset reads the NTC to regulate current — this cell includes that thermistor circuit, so the charger behaves the same as with the original.
• Bench tested on actual hardware: We cycled this cell through full charge and load discharge on a Primo 413. The BMS held stable cutoff at 3.0V under screen-on load and accepted charge without thermal fault. The NTC line stayed within spec throughout.
• Fuel gauge recalibration on first cycle: On first use after fitting, run one complete discharge down to automatic shutdown, then charge uninterrupted to 100% before normal use. The Primo's fuel gauge IC needs one full cycle against the new cell's discharge curve — skip this and the percentage counter will read inaccurately for the first week.

Why the Primo 406 reports wrong battery percentage after a cell swap

The Primo 406 uses a simple coulomb-counting fuel gauge IC that was calibrated to the original cell's impedance and discharge curve. Drop in a fresh cell and that learned curve no longer matches reality. The gauge will typically over-report early on — showing 40% when the phone is close to shutdown — until it relearns the endpoints. One full discharge-to-cutoff followed by an uninterrupted charge to 100% resets the counter against the new cell. After that cycle, percentage readings stabilise.

Sudden shutdown at 20–30% on the replacement cell

This happens when the fuel gauge IC hasn't yet mapped the new cell's voltage cliff. Li-ion cells drop voltage sharply below roughly 3.4V under load — the phone's protection circuit cuts power before the gauge reaches zero. The Primo's screen and RF modem draw enough current during a call or bright-screen use to trigger this cliff earlier than idle readings suggest. Fix it by completing the recalibration cycle described above; the phone needs to see the cell reach its actual low-voltage cutoff — 3.0V — at least once before the gauge adjusts its shutdown threshold.