BLP791 Oppo A72 5G Replacement Battery 3.85V 3900mAh

Oppo A72 5G / A73 5G 2020 — 3.85V Li-Polymer Replacement Battery (BLP791)

This is a 3900mAh (15.02Wh) 3.85V lithium-polymer cell that replaces the BLP791 battery in the Oppo A72 5G 2020, A73 5G 2020, PDYM20, and CPH2161. It powers the phone's processor, display, modem, and cellular radio stack. Swap it when the original cell no longer holds a useful charge or shuts the phone down unexpectedly.

• A72 5G / A73 5G platform fit: Both the A72 5G and A73 5G 2020 share the same battery bay geometry, connector pinout, and BMS handshake protocol — one BLP791 cell covers the full range including PDYM20 and CPH2161 variants.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the A72 5G platform. The BMS accepted the cell on first connection, protection circuits tripped correctly at low-voltage cutoff, and charge current stepped down as expected near full capacity.
• Fuel gauge recalibration after install: On first use after fitting this cell, disable fast charging and run one complete discharge-to-charge cycle at standard speed. This lets the phone's fuel gauge IC map the new cell's discharge curve before high-current fast charging pushes current into an uncalibrated cell.

Sudden shutdown at 20–30% on the replacement cell

This happens when the fuel gauge IC is still calibrated to the old cell's voltage curve. The new cell's voltage drops faster under modem and display load than the IC expects, so it triggers a protective shutdown before the percentage reaches zero. The phone is not faulty and the battery is not defective. Run one full discharge down to automatic shutoff, then charge uninterrupted to 100% — after that cycle the gauge recalibrates and shutdowns at 20–30% stop.

USB fast charge not activating on the first cycle after replacement

Oppo's VOOC charge protocol requires a BMS handshake before the adapter steps up current. On a fresh cell, the BMS may complete this handshake only after the coulomb counter has logged its first full charge cycle. If the phone charges slowly on the first plug-in, that is expected behaviour — not a fault with the charger or the cell. Use the original Oppo adapter and cable, let the first cycle complete at standard current, and VOOC should activate from the second charge onward.