About this replacement
Oppo Reno 5Z 5G 2021 — 3.87V Li-Polymer Replacement Battery (BLP839)
The BLP839 is a 3.87V, 4000mAh Li-Polymer cell for the Oppo Reno 5Z 5G 2021 (CPH2211). It also fits the A94 5G and model 2213. Swap this in when the original cell can no longer hold voltage under 5G modem or display load.
- CPH2211 / A94 5G / 2213 platform fit: These variants share the same 3.87V connector pinout, BLP839 part number, and BMS handshake protocol — one cell covers all three board revisions without modification.
- Bench tested on actual hardware: We ran the BLP839 through full charge and discharge cycles on a CPH2211 board. The BMS accepted charge, reported state-of-charge correctly, and thermal cutoff triggered normally at elevated temps — no flags in the charge IC log.
- Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate against the new cell's discharge curve before high-current charging pushes into an uncalibrated coulomb counter.
Sudden shutdown at 20–30% on the replacement cell
This is a voltage cliff problem, not a capacity problem. The 5G modem and AMOLED panel together draw current spikes the fuel gauge IC hasn't mapped yet on a fresh cell. The old calibration data tells the OS there's charge remaining, but the new cell drops below the cutoff threshold under load before the reported percentage hits zero. Run one full uninterrupted discharge to empty, then charge to 100% without interruption — this resets the coulomb counter to the new cell's actual curve.
USB-PD fast charge not accepted on the first cycle after a cell swap
The Reno 5Z 5G uses Oppo's VOOC charge protocol, which negotiates current limits through the BMS on the new cell. On the first cycle, the charge IC defaults to standard 5V/1A until it completes an internal handshake with the replacement BMS. This is normal behaviour — it is not a fault in the charger or the cable. Charge once at standard rate, let it complete fully, and VOOC fast charge will activate from the second cycle onward.