About this replacement
Oppo Realme Q2 Pro / RMX2173 — 7.74V Li-Polymer Replacement Battery (BLP809)
This is a 7.74V, 2100mAh Li-Polymer replacement battery for the Realme Q2 Pro smartphone (model RMX2173). It carries OEM part number BLP809 and matches the original cell's voltage rail, connector, and physical footprint. The battery fits the standard mid-frame slot without modification.
- RMX2173 platform fit: The Realme Q2 Pro uses a dual-cell Li-Polymer pack at 7.74V nominal — that is two cells in series at approximately 3.87V each. Any replacement must match this voltage configuration exactly, or the charge IC will reject the pack outright. This battery matches that rail.
- Bench tested on actual hardware: We cycled this battery through full charge and discharge on the RMX2173 platform, verified BMS handshake with the charge IC, and confirmed fast-charge protocol acceptance after the first complete cycle. The coulomb counter tracked state of charge without erratic jumps.
- Fuel gauge recalibration on first use: After installing this cell, disable fast charging for the first complete discharge-charge cycle. The fuel gauge IC is still calibrated to the old cell's discharge curve. Running one slow cycle lets it map the new cell's voltage profile before high-current charging begins.
Sudden shutdown at 20–30% on the Realme Q2 Pro after a cell swap
This happens because the fuel gauge IC still holds the old cell's discharge curve in memory. When load spikes — from the modem, display, or background tasks — the new cell's voltage drops faster than the IC expects at that state of charge. The phone reads the voltage drop as a critical low and forces shutdown, even though capacity remains. One full slow discharge to around 3.0V per cell, followed by a full charge, lets the coulomb counter reset against the new cell and eliminates most of these false cutoffs.
USB-PD fast charging not accepted on first cycle after replacement
On first power-up after a cell swap, the charge IC on the Realme Q2 Pro may not negotiate fast-charge protocol with the new BMS. This is a protection behaviour — the IC defaults to trickle charge when it cannot verify cell impedance history. Charge the phone once at standard 5V/1A to completion. On the second cycle, fast charging typically re-negotiates correctly, confirmed at the USB negotiation layer.