Emporia Telme C120 Compatible Battery 3.7V 1200mAh

Emporia Telme C120 / C121 — 3.7V Li-ion Replacement Battery

This is a 3.7V, 1200mAh Li-ion cell for the Emporia Telme C120 and Telme C121. Both are senior-focused basic mobile phones sharing the same battery bay dimensions and connector. Capacity is 4.44Wh, matching the original spec.

• C120 and C121 compatibility: Both models share the same 53.00 × 33.90 × 5.70mm cell footprint and the same single-cell 3.7V charge circuit. No BMS handshake difference exists between the two variants — the same replacement cell fits both.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a C120 unit. The BMS accepted the cell on first insertion, charge current ramped correctly to CC phase, and CV taper completed without fault flags.
• Fuel gauge recalibration on first cycle: After fitting the new cell, run one full discharge to automatic cutoff, then charge uninterrupted to 100%. The C120 uses a simple fuel gauge IC that reads state-of-charge against the previous cell's curve — one full cycle resets that reference to the new cell.

Why the Telme C120 reports wrong battery percentage after a cell swap

The C120's fuel gauge IC builds its percentage model from accumulated charge and discharge data on the old cell. When a new cell goes in, the IC is still referencing the old cell's internal resistance and capacity curve. This mismatch causes the displayed percentage to jump, stall, or read high while the actual cell voltage is already dropping. One full uninterrupted discharge-charge cycle forces the IC to relearn against the new cell's actual discharge profile.

Sudden shutdown at 20–30% on the replacement cell

This happens when the fuel gauge IC hasn't yet recalibrated and the displayed percentage no longer tracks real cell voltage accurately. Under load — an incoming call or screen-on burst — the cell voltage dips sharply, hitting the BMS undervoltage cutoff before the percentage display reaches zero. The phone cuts out even though the screen still shows charge remaining. After the first full recalibration cycle, the gauge aligns with actual voltage and the premature cutoff stops. If it persists past two full cycles, check that charge voltage is reaching 4.2V at the end of the charge phase.