About this replacement
OnePlus Ace 2 Pro — 7.89V Li-Polymer Replacement Battery (BLPA09)
This is a 7.89V, 2400mAh Li-Polymer battery for the OnePlus Ace 2 Pro smartphone. It replaces the original BLPA09 cell when the device no longer holds a charge or shuts down unexpectedly. Restores full functionality across calls, apps, and media without replacing the phone.
- Ace 2 Pro fit: The BLPA09 cell uses a connector and BMS handshake specific to the Ace 2 Pro chassis. The 7.89V nominal voltage matches the dual-cell Li-Polymer configuration the board expects — substituting a different voltage cell will cause the charge IC to reject the pack or report incorrect state-of-charge.
- Bench tested on actual hardware: We cycled this cell through a full charge and discharge on the Ace 2 Pro mainboard. The BMS accepted the pack on first connection, charge IC engaged at the correct 10V VOOC input, and the fuel gauge IC registered cell capacity without manual intervention.
- First-cycle calibration tip: 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 cell — preventing erratic percentage readings early on.
Why the Ace 2 Pro reports wrong battery percentage after a cell swap
The Ace 2 Pro uses a coulomb-counter-based fuel gauge IC that builds its charge model from the original cell's discharge curve. When a new cell goes in, the IC is still reading against the old curve. The result is percentage readings that jump, plateau, or drop faster than expected in the first few cycles. One full slow-charge cycle — charger connected, fast charge off — gives the IC enough data to recalculate the curve against the new cell. After that single cycle, percentage accuracy returns to normal.
Sudden shutdown at 20–30% on the replacement cell
This happens when the fuel gauge IC has not yet mapped the new cell's voltage cliff — the point where cell voltage collapses rapidly under modem or display load. The IC predicts remaining charge from the old curve, so it misses the actual cutoff point on the new cell. The phone shuts down not because the cell is defective, but because the board hits the under-voltage protection threshold (~3.0V per cell) before the OS gets a low-battery warning out. Run one full discharge to automatic shutdown, then charge to 100% without interruption — this resets the cliff mapping in the fuel gauge IC.