K-Touch W70 Replacement Battery 3.7V 1500mAh TBT9608

K-Touch W70 / T87 Series — 3.7V Li-ion Replacement Battery (TBT9608)

This is a 3.7V 1500mAh Li-ion cell built to the TBT9608 specification. It fits the K-Touch W70, W70+, T87, T87+, and four additional variants in the same family. All share the same cell footprint, connector, and voltage rail, so one part number covers the full range.

• W70 and T87 family compatibility: These models share a common PCB layout, identical dock connector pinout, and the same 3.7V nominal charge termination voltage. The BMS handshake is consistent across the W70, W70+, T87, and T87+ variants — no firmware or connector adaptation needed.
• Bench tested on actual hardware: We cycled the TBT9608 cell through charge and discharge on a W70 unit. The BMS accepted charge without fault codes, terminated correctly at 4.2V, and the protection circuit tripped as expected on an over-discharge test below 2.75V per cell.
• Fuel gauge recalibration on first cycle: After fitting this cell, run one full discharge to near shutdown, then charge uninterrupted to 100% before normal use. The W70's fuel gauge IC is calibrated to the old cell's discharge curve — skipping this step produces inaccurate percentage readings for the first several cycles.

Why the W70 reports wrong battery percentage after a cell swap

The W70 uses a coulomb-counting fuel gauge IC that builds its discharge model from previous cell data stored in non-volatile memory. When you swap to a fresh TBT9608 cell, that stored model no longer matches the new cell's actual discharge curve. The gauge reads voltage as a proxy until it accumulates enough cycle data to correct itself. One full discharge and full uninterrupted charge resets the learned curve and brings percentage readings back into alignment.

Sudden shutdown at 20–30% on the replacement cell

This happens when the modem or screen pulls a current spike that the fuel gauge's stored model didn't anticipate for that state of charge. The cell voltage drops momentarily below the BMS cutoff threshold — around 3.0V under load — and the phone shuts off even though the displayed percentage looks safe. It is not a faulty cell. After two or three full discharge-charge cycles, the fuel gauge recalibrates its low-voltage endpoint and the shutdowns stop. If they persist past three cycles, confirm the cell voltage at shutdown is reading above 2.9V with a multimeter probe on the battery terminals.