Doro Primo 365 Replacement Battery RCB01 3.7V 1300mAh

Doro Primo 365 — 3.7V Li-ion Replacement Battery (RCB01)

This is a 3.7V, 1300mAh Li-ion replacement battery for the Doro Primo 365 smartphone. It carries OEM part number RCB01 and slots directly into the phone's battery bay. Capacity is 4.81Wh — matching the original cell specification.

• Primo 365 platform fit: The Primo 365 runs a single-cell 3.7V Li-ion rail with a fixed connector and BMS handshake tied to the RCB01 part number. Any cell outside this voltage and form factor will be rejected by the charge IC or will not seat correctly in the chassis.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Primo 365 platform. The BMS accepted the cell, the charge IC reached full termination voltage without fault flags, and the fuel gauge IC tracked state of charge without dropping into error mode.
• Fuel gauge recalibration after installation: On first use, disable any fast-charge accessory and run one full discharge-charge cycle at standard current. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes current into an uncalibrated state-of-charge register.

Why the Primo 365 reports wrong battery percentage after a cell swap

The Primo 365 uses a fuel gauge IC that stores a learned discharge curve from the original cell. When a new cell goes in, the IC is still reading against the old curve — so it misreports state of charge, often showing full when the cell is not. One complete discharge-charge cycle forces the IC to rewrite its coulomb counter baseline against the new cell's actual chemistry. Until that cycle completes, percentage readings will be inaccurate. After the first full cycle, the gauge should track within a few percent of real capacity.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops sharply under load — the modem or screen draws current, and the cell cannot sustain voltage above the BMS cutoff threshold. The phone reads 25% but the cell is already near its voltage floor under that load spike. The BMS trips the output to protect the cell, and the phone shuts off hard. Let the phone cool for two minutes, then power it on and charge immediately to above 50% before next use — this keeps the cell away from the voltage cliff during high-draw events.