LG G4 Replacement Battery BL-51YF 3.85V 3000mAh Li-ion

LG G4 / H815T / H818P — 3.85V Li-ion Replacement Battery (BL-51YF)

This is a 3000mAh, 3.85V Li-ion battery that replaces part number BL-51YF in the LG G4 and its regional variants including the H815T, H818P, and H818T. It fits the removable battery slot directly and connects to the same three-contact power rail used across the G4 lineup. Capacity figure is 3000mAh / 11.55Wh as specified.

• G4 variant coverage: The G4 was released across multiple carriers and regions under different model codes — H810, H811, H815, H815T, H818P, H818T, and more — but all share the same battery bay dimensions, connector pinout, and BMS handshake. One cell fits the full range.
• Bench tested on actual hardware: We ran this cell in an H815 unit. The BMS accepted the cell without error flags, the charge IC initiated properly, and the fuel gauge began tracking from the first cycle without any manual intervention.
• Fuel gauge recalibration on first use: On first installation, disable fast charging and run one complete discharge-to-charge cycle at standard rate. This lets the G4's fuel gauge IC map the new cell's discharge curve before fast charge pushes higher current into an uncalibrated cell — preventing early percentage-reading errors.

Sudden shutdown at 20–30% on the LG G4 after a cell swap

The G4's Snapdragon 808 processor combined with the AMOLED display can pull brief high-current spikes that a degraded or freshly swapped cell handles differently. If the replacement cell's voltage sags below the BMS cutoff threshold under that load, the phone shuts off even though the fuel gauge still reads 20–30%. This is a voltage-cliff event, not a capacity problem. One full slow discharge-charge cycle lets the coulomb counter recalibrate and typically eliminates this behaviour.

LG G4 not powering on after the battery sat discharged in storage

Li-ion cells stored fully discharged can drop below 2.5V per cell, triggering a BMS lockout that blocks normal charge initiation. When this happens the G4 shows no response — no charging LED, no boot screen. Connect the phone to a wall charger and leave it untouched for 20–30 minutes; the charge IC will attempt a trickle pre-charge to bring the cell back above the BMS recovery threshold. If the cell recovers, the LED activates and normal charging resumes. If there is no response after 45 minutes on a known-good charger, the cell has dropped below safe recovery voltage.