BL-O1 LG K8+ Replacement Battery 3.85V 2900mAh Li-Polymer

LG K8+ / X120 Nova / K20 2019 — 3.85V Li-Polymer Replacement Battery (BL-O1)

This is a 3.85V, 2900mAh Li-Polymer replacement battery for the LG K8+, K8 Plus, X120 Nova, and K20 2019. It carries OEM part numbers BL-O1, EAC64559001, and EAC64619301. It fits directly into these models and restores full device operation when the original cell has degraded or failed.

• K8+ / X120 / K20 2019 platform fit: These models share the same 3.85V single-cell architecture, BL-O1 connector pinout, and BMS handshake protocol. One cell covers the full variant list without modification.
• Bench tested on actual hardware: We cycled this cell on a K8+ unit and monitored BMS communication throughout charge and discharge. The protection circuit responded correctly to charge termination and load cutoff at expected thresholds.
• Fuel gauge recalibration on first use: After installation, run one full discharge down to automatic shutdown, then charge uninterrupted to 100% before enabling fast charge. This gives the fuel gauge IC a clean discharge curve to reference against the new cell — skipping this step is the primary cause of erratic percentage readings in the first week.

Sudden shutdown at 20–30% on the LG K8+ after a cell swap

The K8+ fuel gauge IC stores a learned discharge curve from the original cell. When a new cell goes in, the stored curve no longer matches the actual voltage-versus-capacity profile of the replacement. Under modem transmission or screen-on load, the phone draws a current spike that drops cell voltage below the OS cutoff threshold — even though the coulomb counter still shows charge remaining. The fix is one full uninterrupted discharge-to-shutdown cycle followed by a full charge. After that single cycle, the fuel gauge IC recalibrates and shutdown behaviour normalises.

Fast charge not activating on the first cycle after battery replacement

The K8+ charge IC negotiates fast charge parameters with the BMS on every boot. On a freshly installed cell with no cycle history, the BMS presents high internal impedance and the charge IC defaults to standard 5V/1A to protect the cell. This is expected behaviour, not a fault. Complete one full standard charge cycle and the impedance drops enough for the charge IC to re-enter fast charge negotiation. If fast charge still does not activate after two full cycles, check that the charger output matches the required protocol for this handset.