Motorola Moto G8 Plus KD40 Replacement Battery 3.85V 3800mAh

Motorola Moto G8 Plus (XT2019-1 / XT2019-2) — 3.85V Li-Polymer Replacement Battery (KD40)

This 3800mAh Li-Polymer battery replaces the KD40 cell in the Motorola Moto G8 Plus, covering both XT2019-1 and XT2019-2 variants. It runs at 3.85V nominal and delivers 14.63Wh total energy. Fit it when the original cell no longer holds charge through a full day of use.

• XT2019-1 and XT2019-2 compatibility: Both hardware revisions use the same KD40 cell footprint, voltage rail, and flex connector pinout. The BMS handshake is identical across both variants, so no firmware flag distinguishes them at the battery level.
• Bench tested on actual hardware: We cycled this cell on the XT2019 platform and logged BMS charge acceptance across standard and fast-charge profiles. The protection IC hit expected cutoff voltages at both ends of the charge curve with no anomalous trips.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current fast charging pushes current into an uncalibrated state — preventing erratic percentage readings from the first charge onward.

Sudden shutdown at 20–30% on the G8 Plus after a cell swap

The Moto G8 Plus shuts down under load before the percentage hits zero because the fuel gauge IC is still referencing the discharge curve of the old, degraded cell. A fresh cell holds a steeper voltage cliff at the lower end of its charge window — the phone's modem or screen pull current, voltage sags briefly, and the IC interprets that as a critical low-battery condition. Running one full discharge-charge cycle without fast charging forces the coulomb counter to re-learn the new cell's actual capacity. After that cycle, the shutdown threshold aligns correctly with the real state of charge.

USB-PD fast charge not recognised on the first cycle after replacement

After fitting a new KD40 cell, the G8 Plus sometimes reverts to standard 5V/1A charging on the first plug-in and refuses to negotiate the faster profile. The charge IC gates fast-charge protocol acceptance against the BMS state flags — on a new cell that hasn't completed a full cycle, those flags haven't cleared and the handshake stalls. Charge the phone fully at standard rate first, then let it discharge to around 15–20% before plugging in again. Fast charge negotiation re-establishes at that point once the BMS registers a valid cycle count.