About this replacement
Mobistel Cynus T6 — 3.8V Li-Polymer Replacement Battery (BTY26187)
This is a 3.8V, 4000mAh lithium-polymer battery for the Mobistel Cynus T6 smartphone. It replaces OEM part BTY26187 when the original cell degrades, loses capacity, or no longer holds a charge. Dimensions are 88.10 × 61.53 × 5.95mm — verify against your existing cell before installing.
- Cynus T6 fitment: The T6 uses a dedicated battery bay sized to this exact footprint. The connector pinout matches the OEM BTY26187 layout, so the fuel gauge IC on the motherboard can read cell voltage and temperature data without modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench. The BMS accepted charge current normally, held voltage under screen-on and modem load, and the protection circuit tripped correctly at low-voltage cutoff.
- Fuel gauge recalibration after swap: On first use after installation, disable fast charging and run one full discharge-to-charge cycle. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current charging pushes current into an uncalibrated cell.
Why the Cynus T6 reports wrong battery percentage after a cell swap
The Cynus T6 uses a coulomb counter on the motherboard that was calibrated to the original cell's specific discharge curve. A new cell has a different internal resistance profile, so the counter's charge estimate drifts out of sync immediately. The phone may show 50% while the actual cell state is significantly lower or higher. One full discharge from 100% to automatic power-off, followed by an uninterrupted charge to 100%, resets the reference points the fuel gauge uses.
Sudden shutdown at 20–30% on the replacement cell
This happens when the fuel gauge IC is still running the old cell's voltage-to-capacity map. The new cell hits a voltage cliff under combined modem, screen, and processor load before the OS expects it. The phone reads 25% but the cell voltage drops below the BMS protection threshold — around 3.0V — and the device shuts off to prevent cell damage. Run two full calibration cycles and the reported percentage will align with actual cell state. If shutdowns continue past that point, check that the connector is fully seated and making clean contact on all pins.