Kyocera KX1 Replacement Battery 3.7V 750mAh Li-ion

Kyocera KX1 Series — 3.7V Li-ion Replacement Battery (TXBAT10050 / TXBAT10052)

This 3.7V 750mAh Li-ion cell replaces the original battery in the Kyocera KX1, KX1i, KX1v, and K4130, along with five additional KX-series variants. The OEM part numbers TXBAT10050 and TXBAT10052 cover the same physical cell and connector across this model family. Voltage and capacity specs match factory specification exactly.

• KX1 model family compatibility: The KX1, KX1i, KX1v, and K4130 share the same battery bay dimensions, connector pinout, and BMS handshake protocol. Kyocera issued two OEM part numbers — TXBAT10050 and TXBAT10052 — for the same underlying cell across different regional or carrier variants of these handsets.
• Bench tested on actual hardware: We cycled this cell through charge, full load discharge, and modem-active draw scenarios. The BMS held cutoff voltage correctly at both ends, and the fuel gauge IC registered capacity within the expected range after a full conditioning cycle.
• Fuel gauge recalibration on first cycle: On first use after installation, disable fast charging and run one complete discharge-charge cycle from full to near-empty. This lets the fuel gauge IC map the new cell's discharge curve before any high-current input pushes charge into an uncalibrated state.

Sudden shutdown at 20–30% on the KX1 after a cell swap

The KX1's fuel gauge IC stores the discharge curve of the old, degraded cell in its coulomb counter. When a new cell is installed, that stored curve no longer matches the actual voltage behaviour of the fresh cell. The phone interprets the voltage drop under modem or screen load as a near-empty state and cuts power even though charge remains in the cell. One full uninterrupted discharge-charge cycle forces the IC to re-learn the new curve and stops the premature shutdown.

Phone not powering on after the replacement battery sat in storage

Li-ion cells self-discharge in storage. If voltage drops below approximately 2.5V per cell, the BMS enters a lockout state and blocks normal charging to prevent damage to an over-discharged cell. Plugging in via USB may show no charge indicator at all. Apply a five-to-ten minute trickle charge using the original wall adapter — not a fast charger — and the BMS should release lockout once the cell recovers above 3.0V, at which point normal charging resumes.