Kyocera TXBAT10052 KOI Replacement Battery 3.7V 750mAh

Kyocera KOI / KX2 / SoHo — 3.7V Li-ion Replacement Battery (TXBAT10052)

This 3.7V 750mAh Li-ion cell replaces the original battery in the Kyocera KOI, KX2, and SoHo handsets. All three share the same battery bay, connector, and BMS communication protocol. Capacity is 750mAh (2.78Wh), matching the original specification.

• KOI, KX2, and SoHo compatibility: These three Kyocera models run the same voltage rail and use an identical physical connector and BMS handshake. One cell fits all three without modification.
• Bench tested on actual hardware: We cycled this cell through a full charge and load discharge on a KOI unit. The BMS accepted the cell without fault codes and the charge IC held a steady taper current to 4.2V cutoff.
• Fuel gauge recalibration on first use: After fitting this cell, run one complete discharge down to auto-shutoff before recharging. The KOI's fuel gauge IC calibrates its coulomb counter against the first full discharge curve — skipping this step causes erratic percentage readings for the first several days of use.

Sudden shutdown at 20–30% on the KOI after a cell swap

The KOI's fuel gauge IC stores a discharge curve calibrated to the old cell. When a new cell with different internal impedance goes in, the IC's voltage-to-percentage map is wrong. Under modem or screen load, voltage drops faster than the IC expects, and the phone shuts off before it reads zero. One full discharge-recharge cycle forces the IC to relearn the new cell's curve. After that cycle, shutdowns at 20–30% stop.

Phone shows full charge but dies within minutes of unplugging

This happens when the original cell has degraded to the point where it accepts a charge current and reaches 4.2V quickly — giving the illusion of a full charge — but actual capacity is a fraction of rated 750mAh. The charge IC measures voltage, not capacity. Swapping in a fresh 750mAh cell and running one full discharge cycle will restore accurate percentage reporting. Confirm recovery by checking that the phone sustains voltage above 3.6V under screen-on load.