LG G5 Replacement Battery BL-42D1F 3.8V 1900mAh

LG G5 / H830 / H840 — 3.8V Li-ion Replacement Battery (BL-42D1F)

This is a 3.8V, 1900mAh Li-ion cell replacing the BL-42D1F battery in the LG G5 and its variants, including the H830, G5 Lite, and H840. The G5 uses a removable battery — one of the few flagships of its era to do so — making cell swaps straightforward without special tools. This replacement matches the original voltage and form factor to seat flush in the battery bay.

• G5 series compatibility: The G5, H830, G5 Lite, and H840 all share the same battery bay geometry, connector pin-out, and BMS handshake protocol. LG used a consistent 3.8V rail across this lineup, so one cell covers the full model range without modification.
• Bench tested on actual hardware: We ran this cell on G5 hardware and monitored the BMS through a full charge-discharge cycle. The charge IC accepted the cell without triggering a fault, and the protection circuit responded correctly to load spikes from the Snapdragon 820 during sustained CPU activity.
• Fuel gauge recalibration on first use: After installing this cell, disable fast charging for the first complete discharge-charge cycle. The G5's fuel gauge IC needs to map the new cell's discharge curve before it can report accurate percentages — skipping this step with fast charging active can push current into an uncalibrated state and produce erratic percentage readings.

Why the G5 reports wrong battery percentage after a cell swap

The G5 uses a coulomb counter and fuel gauge IC that stores a learned discharge curve from the previous cell. When a new cell goes in, that stored curve no longer matches actual cell chemistry and capacity. The OS reads percentage from the fuel gauge IC, not raw voltage, so it reports whatever the stale curve says — which can be off by 15–25%. One full discharge to automatic shutdown followed by an uninterrupted charge to 100% forces the IC to relearn the curve against the new cell.

Sudden shutdown at 20–30% remaining on the replacement cell

This happens when the cell voltage drops below the modem's or display's minimum operating threshold under load, even though the fuel gauge still shows charge remaining. The G5's Snapdragon 820 with simultaneous LTE, screen-on, and GPS can draw enough current to cause a brief voltage sag that triggers hardware shutdown — the BMS reads this as a protection event, not a low-battery event. The fuel gauge IC hasn't yet calibrated the voltage-to-percentage mapping for the new cell, so 25% on-screen may actually represent a voltage level that can't sustain peak draw. Run one full recalibration cycle; if shutdowns persist, check cell voltage under load with a meter — it should not drop below 3.4V during normal screen-on use.