BLP759 OnePlus 8 Pro Replacement Battery 3.85V 3900mAh

OnePlus 8 Pro / IN2020 — 3.85V Li-Polymer Replacement Battery (BLP759)

This is a 3.85V, 3900mAh (15.02Wh) Li-Polymer cell built to the BLP759 specification for the OnePlus 8 Pro and 8 Pro 5G (IN2020, IN2021). It replaces the original cell when capacity has degraded from normal charge cycles and the phone can no longer hold charge through a full day of use. The connector and cell dimensions — 74.20 x 63.94 x 4.80mm — match the original bay without modification.

• 8 Pro and 8 Pro 5G compatibility: Both the standard 8 Pro and 5G variants (IN2020, IN2021) use the same BLP759 cell, voltage rail, and BMS handshake. The 5G modem draws from the same power path, so one part number covers both board revisions.
• Bench tested on actual hardware: We cycled this cell on an IN2020 board and confirmed the BMS accepted the cell without fault codes. The charge IC completed a full CC-CV cycle and the fuel gauge IC logged the new cell's discharge curve across two full cycles.
• First cycle after installation: Disable Warp Charge for the first complete discharge-charge cycle. This lets the fuel gauge IC build a baseline discharge curve against the new cell before high-current fast charging pushes current into an uncalibrated coulomb counter — it prevents erratic percentage readings in the first week.

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

After a cell swap, the OnePlus charge IC sometimes refuses to enter Warp Charge mode on the first session. The BMS on the new cell starts in a conservative protection state and the charge IC falls back to standard 5V charging until it sees a completed cycle. This is not a wiring fault. Run one full standard-rate charge to 100%, then discharge naturally — Warp Charge re-enables once the BMS exits its initial protection window.

Sudden shutdown at 20–30% remaining after the swap

This happens when the fuel gauge IC is still running the discharge curve from the old, degraded cell. The new cell's actual voltage drops below the IC's expected floor at 20–30% reported charge, triggering a protective shutdown before the display reaches 0%. The fix is one full uninterrupted discharge-charge cycle at standard rate — no top-ups mid-drain. After that cycle, the coulomb counter recalibrates to the new cell's voltage curve and the shutdowns stop. If they persist past two cycles, check that the flex connector is seated flat at both ends.