BTR741B Casio GzOne Brigade Compatible Battery 3.7V 1200mAh

Casio GzOne Brigade C741 / C731 Rock — 3.7V Li-ion Replacement Battery (BTR741B)

This is a 3.7V, 1200mAh Li-ion replacement battery for the Casio GzOne Brigade, GzOne Brigade C741, and GzOne C731 Rock. All three are rugged phones that share the same BTR741B battery slot, connector, and BMS handshake. Capacity comes direct from product data: 4.44Wh.

• GzOne Brigade and C731 Rock compatibility: These three models share the same battery bay dimensions, 3.7V voltage rail, and identical connector pinout. The BMS handshake is the same across the lineup, so one cell covers all three without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the GzOne Brigade platform. The BMS accepted the cell cleanly, held voltage through screen-on and radio-active loads, and did not trigger overcurrent cutoff during normal call and data use.
• Fuel gauge recalibration on first use: After fitting this cell, disable fast charging and run one full discharge-charge cycle from 100% down to auto-shutdown and back to full. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging pushes current into an uncalibrated state.

Why the GzOne Brigade reports wrong battery percentage after a cell swap

The GzOne Brigade uses a fuel gauge IC that stores a discharge curve calibrated to the original cell. When you fit a new cell, that stored curve no longer matches the actual voltage-to-capacity relationship of the replacement. The phone reads voltage and translates it to a percentage using the old map — so the number on screen drifts from reality. One complete discharge cycle, letting the phone shut itself down at low battery, then charging uninterrupted to 100% resets the counter and syncs the gauge to the new cell.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops sharply under modem or screen load — a voltage cliff the fuel gauge did not predict. The phone reads 25% but the cell cannot hold voltage above the cutoff threshold when the radio draws peak current, so the BMS trips and the device shuts down. It is not a faulty cell — it is the fuel gauge IC still running on an old calibration. Run one full discharge-charge cycle and check that the shutdown threshold resets. If the phone still cuts out below 3.2V under load after two cycles, check that the battery contacts are clean and seated flush.