Mobistel Cynus F6 BTY26188 Replacement Battery 3.8V 2000mAh

Mobistel Cynus F6 — 3.8V Li-ion Replacement Battery (BTY26188)

This is a 3.8V, 2000mAh Li-ion cell sized to fit the Mobistel Cynus F6 smartphone. It replaces the original BTY26188 battery when the existing cell no longer holds a usable charge. The battery matches the factory dimensions of 72.05 × 57.01 × 4.35mm and connects through the same board connector.

• Cynus F6 fitment: The BTY26188 is specific to this handset — the cell footprint, connector tab position, and BMS communication protocol are matched to the Cynus F6 power management IC. No adapter or modification is needed.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on a Cynus F6 unit, confirming BMS handshake, thermal sensor response, and that the charge IC accepted the cell without fault codes.
• Fuel gauge recalibration on first cycle: After fitting, run one full discharge to the auto-shutdown point, then charge uninterrupted to 100% before normal use. This gives the fuel gauge IC accurate endpoints to map the new cell's discharge curve, which cuts erratic percentage readings from the first day.

Why the Cynus F6 reports wrong battery percentage after a cell swap

The Cynus F6 uses a coulomb counter in the fuel gauge IC that builds its model against the previous cell's charge curve. When a new cell goes in, the stored curve no longer matches the actual discharge behaviour, so the percentage display drifts — sometimes reading 40% and shutting down seconds later. The fix is one complete uninterrupted discharge-to-shutdown followed by a full charge to 100%. After that cycle, the IC has real endpoints from the new cell and percentage readings stabilise. Do not interrupt this first cycle with a mid-charge top-up.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff failure, not a capacity problem. Under modem load or screen-on draw, the cell voltage drops sharply below the BMS cutoff threshold — typically around 3.2V — before the fuel gauge reports 0%. The phone sees an undervoltage condition and cuts power to protect the cell. If shutdowns happen consistently around the same percentage, charge the phone to 100%, then run a full single discharge cycle to let the fuel gauge remap the voltage-to-percentage curve. If shutdowns persist below 3.3V under load after two full cycles, the cell replacement has been completed correctly and the issue is in the modem or display draw — check background app activity first.