TeXet TD-D109 B111 Replacement Battery 3.7V 900mAh

TeXet TD-D109 Series — 3.7V Li-ion Replacement Battery (B111)

This is a 3.7V, 900mAh Li-ion cell built to fit the TeXet TD-D109 and related handsets including the TM-B111, TM-B210, and TM-B310. It replaces the original B111 battery when the existing cell has degraded, swells, or no longer holds a usable charge. Voltage and capacity match the OEM specification exactly.

• TD-D109 and TM-B series compatibility: These models share the same battery bay dimensions, connector pinout, and 3.7V nominal voltage rail. The BMS handshake is consistent across the series, so the same cell fits without modification.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the TD-D109 platform. The BMS accepted the cell on first insertion, reported charge state correctly after one full cycle, and thermal output during charging stayed within normal range for a 900mAh cell.
• Fuel gauge recalibration on first cycle: After fitting this replacement, disable fast charging and run one complete discharge-charge cycle at standard rate. The phone's fuel gauge IC is still calibrated to the old cell's discharge curve — one full cycle at low current lets it recalibrate before high-current charging begins.

Why the TD-D109 reports wrong battery percentage after a cell swap

The fuel gauge IC in the TD-D109 tracks battery state using a coulomb counter anchored to the previous cell's discharge curve. When you swap in a new cell, that reference is stale. The phone may show 100% immediately after installation or drop percentage faster than expected in the first few sessions. One full discharge-charge cycle at standard current resets the coulomb counter baseline. After that cycle, percentage readings stabilise.

Sudden shutdown at 20–30% charge remaining

This happens when the cell voltage drops below the modem or screen load threshold before the displayed percentage reaches zero — a voltage cliff rather than a true empty state. It is common on a fresh cell before the fuel gauge has a calibrated discharge curve, and also appears on cells that have degraded past ~70% of original capacity. Run one full discharge to automatic shutdown, then charge uninterrupted to 100% without interruption. If shutdowns continue past two full cycles, check that the resting voltage after a full charge reads at least 4.1V.