About this replacement
BQ Aquaris M5 — 3.8V Li-Polymer Replacement Battery (3120)
This 3.8V, 3000mAh Li-Polymer battery is a direct cell replacement for the BQ Aquaris M5 smartphone. It matches the OEM part number 3120 and fits the physical bay with the same 71.76 × 59.28 × 4.62 mm footprint. Capacity is rated at 11.4Wh, matching the original specification.
- Aquaris M5 fitment: The M5 uses a flat Li-Polymer pouch cell with a specific connector orientation tied to the device's charge IC. This cell matches that connector pinout and the BMS handshake expected by the Aquaris M5 power management unit — no adapter or modification needed.
- Bench tested on actual hardware: We cycled this cell through full charge and discharge on the Aquaris M5 platform. The BMS accepted the cell without fault codes, charge current ramped correctly through CC/CV stages, and the fuel gauge IC tracked state-of-charge without erratic jumps after the first full cycle.
- First-cycle fuel gauge reset: After fitting this cell, disable fast charging in settings and complete one full discharge-to-charge cycle before resuming normal use. This lets the fuel gauge IC recalibrate its coulomb counter against the new cell's actual discharge curve before high-current charging loads the system.
Why the Aquaris M5 reports wrong battery percentage after a cell swap
The Aquaris M5 uses a fuel gauge IC that stores a learned discharge curve from the previous cell. When a new cell goes in, that stored curve no longer matches the actual electrochemical behaviour of the replacement. The gauge reads voltage and estimates charge state against old data, so it can report 40% when the cell is close to cutoff. One complete discharge-charge cycle forces the IC to rewrite its reference curve against the new cell. After that cycle, percentage reporting stabilises.
Sudden shutdown at 20–30% on the Aquaris M5 after replacement
This happens when the fuel gauge IC has not yet calibrated to the new cell's voltage cliff. Li-Polymer cells drop voltage sharply below a certain state-of-charge threshold — on a miscalibrated gauge, the OS still shows 25% when the cell voltage has already fallen below the modem's minimum rail. The SoC kills power to protect the hardware before the user sees 0%. Run one full discharge until the phone powers off naturally, then charge uninterrupted to 100% — this anchors both the low and high endpoints of the coulomb counter.