Alcatel OT-S210 Replacement Battery 3.7V 600mAh Li-ion

Alcatel OT-S210 / OT-S211 Series — 3.7V Li-ion Replacement Battery (CAB2001010C1)

This is a 3.7V, 600mAh Li-ion cell for the Alcatel OT-S210, OT-S211, OT-S211C, and One Touch S210 series. These are compact candybar-style mobile phones from the mid-2000s whose original batteries have aged past useful capacity. OEM part numbers CAB2001010C1, OT-BY25, B-U81, and CAB2001011C1 all cross to this cell.

• OT-S210 and OT-S211 shared battery platform: These models use the same 37 × 37 × 5.10mm cell footprint, identical connector orientation, and the same BMS handshake voltage threshold — so one cell covers the full S210/S211 family without modification.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the OT-S211. The BMS accepted charge correctly, protection tripped cleanly at the low-voltage cutoff, and the phone powered through calls and SMS without sagging off.
• Fuel gauge recalibration after installation: The OT-S210 series uses a basic fuel gauge IC that tracks coulombs against the original cell's discharge curve. After fitting a new cell, run one complete discharge down to auto-shutdown, then charge uninterrupted to 100% before normal use — this resets the gauge to the new cell's actual capacity.

Why the OT-S210 reports wrong battery percentage after a cell swap

The phone's fuel gauge IC builds its capacity model from the discharge curve of whichever cell was installed at the factory. Swap in a fresh cell and that model is now mismatched — the IC is counting coulombs against a curve that no longer applies. The percentage reading becomes unreliable until recalibration happens. One full discharge-to-shutdown followed by a complete uninterrupted charge cycle forces the IC to rewrite its reference curve against the new cell.

Phone shuts down suddenly while showing 20–25% remaining

This is a voltage cliff issue. At around 3.5–3.6V, an aged or uncalibrated cell cannot sustain voltage under the current draw of an active call or screen backlight — the terminal voltage drops sharply and the phone's low-voltage cutoff fires before the gauge reaches 0%. A fresh cell with a correctly calibrated fuel gauge eliminates this because the actual resting voltage at 20% is now higher and stable. If the shutdown persists after one full calibration cycle, check that the cell is seated flush and the contact pads are clean — poor contact adds resistance that accelerates voltage sag.