K-Touch U86 Replacement Battery TBW5931 3.7V 1600mAh

K-Touch U86 / E616 — 3.7V Li-ion Replacement Battery (TBW5931)

This is a 3.7V, 1600mAh Li-ion cell replacing the original TBW5931 battery in the K-Touch U86 and E616 smartphones. It fits the existing battery bay without modification. Voltage and physical dimensions match the OEM spec exactly.

• U86 and E616 platform fit: Both models share the TBW5931 footprint — same 60.48 × 56.85 × 4.50 mm envelope, same 3.7V nominal rail, and the same three-contact connector layout. One cell covers both devices.
• Bench tested on actual hardware: We cycled this cell through charge, standby draw, and screen-on load. The BMS held cutoff at the correct low-voltage threshold and did not trip under normal display and modem current draw.
• Fuel gauge recalibration on first use: On first installation, disable fast charging if the option is available and run one full discharge down to auto-off, then charge uninterrupted to 100%. This gives the fuel gauge IC one complete cycle to map the new cell's discharge curve before reporting accurate percentages.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff problem, not a capacity defect. When the modem transmits or the screen peaks in brightness, current draw spikes sharply. A new cell with an uncalibrated fuel gauge IC can hit the BMS low-voltage cutoff — typically around 3.0V per cell — while the OS still shows 20–30% remaining. The reported percentage and the actual cell voltage are out of sync. One full discharge-to-auto-off cycle followed by an uninterrupted charge to 100% resyncs the coulomb counter and eliminates most cliff shutdowns.

OS percentage jumping erratically after swap

The fuel gauge IC on the K-Touch U86 learns cell behaviour from charge and discharge history stored against the old cell's impedance profile. After a cell swap, that stored profile no longer matches the new cell, so the reported percentage bounces — sometimes gaining or losing 10–15% in seconds. This is not a fault with the replacement cell. Run two complete discharge and charge cycles without interrupting the charge phase, and the IC rebuilds an accurate model against the new cell. After the second cycle, percentage readings stabilise; verify by checking that the phone reads above 4.1V at reported 100%.