LG BL-T19 H791 Replacement Battery 3.8V 2600mAh

LG Nexus 5X / H791 — 3.8V Li-Polymer Replacement Battery (BL-T19)

This is a 3.8V, 2600mAh Li-Polymer cell built to replace the BL-T19 in the LG Nexus 5X (H791, H791F, Bullhead). It fits the same physical cavity — 67.80 × 53.64 × 4.70 mm — and connects to the same charge IC the original cell used. If your Nexus 5X is shutting down unexpectedly or refusing to hold charge, the BL-T19 is the likely culprit.

• Nexus 5X / Bullhead platform fit: The H791, H791F, and Bullhead variants all run the same power rail and BMS handshake. They share the BL-T19 footprint and connector pinout, so one cell works across the full H791 lineup without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on an H791 unit. The BMS accepted the cell without flagging a protection fault, and the charge IC transitioned cleanly from constant-current to constant-voltage at 4.35V.
• First-cycle fast charge behaviour: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate its coulomb counter against the new cell's discharge curve before high-current charging pushes into an uncalibrated state.

Why the Nexus 5X reports the wrong battery percentage after a cell swap

The Nexus 5X uses a coulomb-counter fuel gauge IC that tracks charge by measuring current in and out of the original cell. When you install a new cell, the IC still references the old discharge curve stored in its memory. The percentage display will drift — sometimes reading 80% when the actual state of charge is closer to 50%. One full discharge down to automatic shutdown, followed by an uninterrupted charge to 100%, forces the IC to remap its curve to the new cell. After that cycle, the percentage readout tracks accurately.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage-cliff issue, not a capacity problem. Under combined modem and screen load, the cell voltage can drop sharply at around 3.6V — faster than the fuel gauge IC anticipates — triggering an undervoltage shutdown even though the displayed percentage still looks safe. It almost always appears in the first few cycles before the IC has recalibrated. Run two full discharge-charge cycles without fast charging, and the shutdowns stop. If they continue past cycle three, check that cell voltage at shutdown is above 3.4V — below that points to a seating or connector issue rather than calibration.