KX50 Motorola Moto G Pro Replacement Battery 3.85V 3900mAh

Motorola Moto G Pro / G8 Pro — 3.85V Li-Polymer Replacement Battery (KX50)

The KX50 is a 3.85V lithium-polymer cell rated at 3900mAh (15.02Wh), built to fit the Motorola Moto G Pro (XT2043-8), Moto G8 Pro, and Moto G8 Stylus. It slots into the same battery bay as the original and connects to the same charge IC and fuel gauge circuit. Capacity figures come from the product data, not web estimates.

• Moto G Pro / G8 series compatibility: These models share the KX50 battery platform — same 3.85V nominal rail, same connector pinout, and the same BMS handshake expected by Motorola's charge IC. A cell mismatch here triggers charge IC refusal, not just slow charging.
• Bench tested on actual hardware: We ran this cell through charge-discharge cycles on a Moto G Pro unit and logged BMS response at full draw — display, modem, and GPS active simultaneously. The protection circuit held cutoff at the correct lower threshold without tripping on load spikes.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard rate. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current sessions push charge into an uncalibrated coulomb counter.

Sudden shutdown at 20–30% on the Moto G Pro after a cell swap

This happens when the fuel gauge IC is still reading the old cell's voltage curve. The new KX50 cell hits a steeper voltage drop under modem and display load than the worn original did — the phone interprets that sag as a critically low state and shuts down. The fix is one full discharge to auto-off, then a full charge without interruption. After that cycle, the coulomb counter realigns to the new curve and the reported percentage tracks actual cell voltage correctly.

USB-PD fast charge not accepted on first cycle after replacement

Some units refuse fast-charge negotiation on the first cycle after installing a new cell because the charge IC defaults to a conservative profile until it sees a completed charge-discharge loop. The phone may show standard charging speed or no fast-charge indicator at all. Charge once at standard rate to 100%, then discharge under normal use. Fast-charge negotiation typically resumes from the second cycle once the IC confirms the new cell's internal resistance profile is within range.