Mobistel Cynus T7 Replacement Battery BTY26186 3.7V 1800mAh

Mobistel Cynus T7 / MT-600S / MT-600W — 3.7V Li-Polymer Replacement Battery (BTY26186)

This is a 3.7V, 1800mAh lithium-polymer replacement battery for the Mobistel Cynus T7, MT-600S, and MT-600W smartphones. It matches the original BTY26186 cell dimensions at 92.10 × 62.52 × 4.50mm, so it seats correctly in the battery bay without modification. Swap it in when the original cell no longer holds a useful charge.

• Cynus T7, MT-600S, MT-600W compatibility: All three models share the same 3.7V single-cell architecture, battery connector pinout, and BMS handshake protocol — which is why one cell covers the whole group without adapter or modification.
• Bench tested on actual hardware: We cycled this cell through a full discharge and charge sequence on the MT-600 platform. The BMS accepted the charge curve without fault flags, and the fuel gauge IC began tracking state-of-charge correctly after one complete cycle.
• First-cycle fuel gauge recalibration: After installation, disable fast charging and run one full discharge down to automatic shutoff, then charge uninterrupted to 100%. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging sessions begin.

Sudden shutdown at 20–30% on the Cynus T7 after a cell swap

This happens because the fuel gauge IC is still running the discharge curve it learned from the old, degraded cell. The new cell has a steeper voltage cliff at the lower end of its charge window, and the IC hasn't mapped it yet. When the modem fires a burst transmission or the screen ramps brightness, current draw spikes and the cell voltage drops below the BMS cutoff threshold — even though the reported percentage looks safe. One complete discharge-charge cycle without interruption resets the coulomb counter and eliminates these shutdowns.

Phone reports incorrect battery percentage after replacement

The Cynus T7's fuel gauge IC stores calibration data tied to the previous cell's internal resistance and capacity fade profile. A fresh 1800mAh cell has different impedance characteristics, so the IC's percentage readings drift — often showing 100% that drops sharply to 60% within minutes, or freezing near 20% before cutting out. Force a full calibration cycle: drain the phone to automatic shutdown, then charge to 100% on a standard 5V charge with fast charging off. After that single cycle, percentage reporting stabilises against the new cell's actual discharge curve.