TXBAT0C02 Kyocera KZ820 Compatible Battery 3.7V 750mAh

Kyocera KZ820 / KZ850 Series — 3.7V Li-ion Replacement Battery (TXBAT0C02)

This is a 3.7V, 750mAh Li-ion cell built to the TXBAT0C02 specification. It fits the Kyocera KZ820, KZ830, KZ850, and QCP-2135, among others. Swap it in when the original cell no longer holds enough charge to keep the phone running through normal daily use.

• KZ820 / KZ830 / KZ850 platform fit: These models share the same battery bay geometry, connector pinout, and BMS handshake protocol — all built around the same TXBAT0C02 footprint. One cell covers the full range without adapter or modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the KZ850 platform. The BMS accepted the new cell on first insertion, charge termination triggered correctly at 4.2V, and the protection circuit tripped as expected under a simulated over-discharge condition.
• Fuel gauge recalibration on first install: After fitting this cell, run one full discharge to 10% or lower, then charge uninterrupted to 100% before resuming normal use. The phone's coulomb counter is calibrated to the old cell's discharge curve — skipping this step causes the OS to report inaccurate percentages from day one.

Sudden shutdown at 20–30% on the replacement cell

This happens because the fuel gauge IC still maps percentage readings to the old cell's voltage curve. When the new cell's actual terminal voltage drops under modem transmit or screen load, it hits the low-voltage cutoff before the OS registers critical battery level. The phone shuts off while the display still reads 25%. One full discharge-to-10% followed by a complete charge cycle forces the coulomb counter to re-anchor its 0% threshold to the new cell's actual floor voltage — typically around 3.0V under load for this chemistry.

Phone warm near the battery during the first few charge cycles

A new Li-ion cell has higher internal impedance than a broken-in cell. The charge IC pushes the same current into a higher-resistance load, and that difference dissipates as heat near the battery compartment. This is normal for the first three to five cycles as the cell's impedance settles. If the phone still runs noticeably warm after five full cycles, check that the battery connector is fully seated — a partially engaged pin increases contact resistance and compounds the heat.