TeXet TM-333 TB-BL4U Compatible Battery 3.7V 1200mAh

TeXet TM-333 / TM-D305 — 3.7V Li-ion Replacement Battery (TB-BL4U)

This is a 3.7V, 1200mAh Li-ion replacement cell for the TeXet TM-333 and TM-D305 smartphones. It matches the OEM part number TB-BL4U and fits the original battery compartment at 62.00 × 38.00 × 4.50mm. Swap it when the original cell no longer holds a charge or causes unexpected shutdowns.

• TM-333 and TM-D305 compatibility: Both models share the same 3.7V single-cell architecture, connector pinout, and BMS handshake protocol — a single TB-BL4U cell covers both without modification.
• Bench tested on actual hardware: We cycled this cell through a full discharge and charge sequence on the TM-333, confirming the BMS accepted the cell, reported state-of-charge correctly, and did not trigger an over-voltage cutoff on completion.
• First-cycle calibration tip: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate against the new cell's discharge curve before high-current charging pushes current into an uncalibrated state.

Why the TM-333 reports wrong battery percentage after a cell swap

The TM-333 uses a fuel gauge IC that builds its discharge model from the previous cell's coulomb counter history. When a new cell goes in, the IC is still referencing the old degraded curve. The result is a percentage reading that doesn't match actual charge state — often showing 100% shortly after plugging in, then dropping fast. One full discharge-charge cycle resets the counter and aligns the gauge to the new cell's actual capacity.

Sudden shutdown at 20–30% on the replacement cell

This happens when the fuel gauge IC hasn't finished recalibrating and the phone hits a voltage cliff under modem or screen load. The cell voltage drops sharply below the shutdown threshold even though the gauge still shows charge remaining. It's not a faulty cell — it's the IC acting on stale data. Run two full discharge-charge cycles without interruption and the shutdowns will stop as the coulomb counter resets to the new cell's actual floor voltage, typically around 3.4–3.5V under load.