About this replacement
Motorola Moto G9 Plus / Moto E6 Play (US) — 3.85V Li-Polymer Replacement Battery (KS40)
This is a 3.85V, 2750mAh lithium-polymer replacement battery for the Motorola XT2029-1 (Moto G9 Plus) and Moto E6 Play (US). It replaces OEM part numbers KS40 and SB18C51767. Swap it in when the original cell no longer holds a useful charge or the phone shuts down unexpectedly.
- XT2029-1 and Moto E6 Play compatibility: Both models share the KS40 cell format — same 3.85V nominal rail, same connector pinout, and the same BMS handshake protocol. One cell covers both devices without modification.
- Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on the XT2029-1 platform. The BMS accepted the cell cleanly, charge termination triggered correctly at 4.35V, and voltage held stable under display and modem load without triggering overcurrent cutoff.
- First-cycle fast charge disable: On first use after installation, turn off fast charging for one complete discharge-charge cycle. The fuel gauge IC is calibrated to the old cell's discharge curve — letting it complete one slow cycle against the new cell recalibrates the coulomb counter before high-current charging begins.
Sudden shutdown at 20–30% on the replacement cell
This happens because the fuel gauge IC still holds the discharge curve from the degraded original cell. When the new cell's voltage drops under modem or screen load, the phone hits a voltage cliff the IC wasn't expecting and cuts power to protect the SoC. It is not a defective cell — it is a calibration mismatch. Run two full discharge-charge cycles with fast charging disabled and the shutdowns will stop. After calibration, the low-battery cutoff will track correctly at approximately 3.4V under load.
USB-PD fast charge not working on the first cycle after replacement
After a cell swap, the charge IC may default to trickle charge on the first cycle while it confirms BMS handshake with the new cell. This is normal behaviour on the G9 Plus platform and does not mean the battery or charger is faulty. Use the original Motorola TurboPower adapter and complete one full slow charge from under 10% to 100% without interruption. Fast charging typically resumes on the second cycle once the charge IC accepts the new cell's impedance profile.