Samsung Galaxy M11 HQ-S71 Replacement Battery 3.85V 4900mAh

Samsung Galaxy M11 — 3.85V Li-Polymer Replacement Battery (HQ-S71)

This is a 3.85V, 4900mAh lithium-polymer replacement battery for the Samsung Galaxy M11 (SM-M115F/DS). It carries OEM part numbers HQ-S71 and GH81-18734A and fits the M11 2020 variant. The cell slots into the same physical bay and connects to the same power management IC as the original unit.

• Galaxy M11 and SM-M115 series fit: All SM-M115 variants share the same 3.85V power rail, connector pinout, and BMS handshake protocol. One replacement cell covers the full model range without adapter or modification.
• Bench tested on actual hardware: We ran this cell through the Galaxy M11's charge IC and confirmed the BMS accepted the handshake, passed thermal checks, and held voltage under display and modem load without triggering a protection cutoff.
• Fuel gauge recalibration on first use: After installing this cell, disable fast charging and run one full discharge-to-charge cycle at standard rate. This lets the fuel gauge IC map its coulomb counter against the new cell's discharge curve before high-current charging introduces error into an uncalibrated state.

Sudden shutdown at 20–30% on the Galaxy M11 after a cell swap

This happens because the fuel gauge IC is still using the discharge curve it learned from the old, degraded cell. A new cell holds a steeper voltage cliff at the lower end of its range. When the modem fires a high-power transmission or the display peaks brightness, the cell voltage drops sharply — the IC reads this as a critically low state and triggers a shutdown before the percentage gauge catches up. One complete slow-charge cycle recalibrates the coulomb counter to the new cell's actual curve and eliminates the early cutoff.

USB fast charge not activating on the first cycle after replacement

On the first connection after a cell swap, the charge IC runs a brief BMS authentication check before enabling the higher voltage negotiation required for fast charging. If the cell's state-of-charge is below roughly 3.6V per cell, the IC defaults to trickle mode and will not step up to fast charge until a baseline voltage is reached. Plug into a standard 5V charger first and let the phone reach around 15% charge. After that point, fast charging protocols re-engage normally on subsequent connections.