About this replacement
Samsung Galaxy Mega 5.8 / GT-I9150 — 3.7V Li-ion Replacement Battery (B650AE)
This is a 3.7V, 2100mAh Li-ion replacement battery for the Samsung Galaxy Mega 5.8 and Galaxy Mega Duos smartphones. It fits GT-I9150 and GT-I9152 variants using OEM part numbers B650AE and B650AC. Swap it in when your original cell no longer holds a charge through a normal day.
- GT-I9150 and GT-I9152 compatibility: Both the standard Mega 5.8 and the Duos dual-SIM variant use the same 3.7V battery bay, connector pinout, and BMS handshake — one cell fits both boards without modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the GT-I9150 board. The BMS accepted the cell on first connection, charge termination triggered correctly at 4.2V, and the fuel gauge IC reported capacity without error codes.
- Fuel gauge recalibration after install: On first use, disable any power-saving fast-charge modes and run one complete discharge-to-charge cycle without interruption. This lets the fuel gauge IC map its coulomb counter against the new cell's discharge curve before the system starts making power decisions based on stored data from the old cell.
Sudden shutdown at 20–30% on the Galaxy Mega 5.8
This is a voltage cliff issue, not a capacity issue. The Mega 5.8 runs a large 5.8-inch display alongside dual-SIM radio activity, which pulls current in short, heavy bursts. When the cell voltage sags below roughly 3.4V under that load, the BMS trips a cutoff to protect the cell — even if the fuel gauge still shows charge remaining. A fresh cell with lower internal resistance holds voltage under that load better than a worn original. If shutdowns continue after replacing the cell, run one full calibration cycle to sync the fuel gauge IC to the new cell's voltage curve.
Battery percentage jumping erratically after fitting the new cell
The Galaxy Mega 5.8 stores its fuel gauge calibration data against the discharge curve of the previous cell. After a cell swap, the coulomb counter reads voltage points that no longer match its stored reference table, so the percentage display jumps. This is not a fault with the replacement cell. Fully discharge the phone until it powers off, then charge uninterrupted to 100% — this forces the fuel gauge IC to rewrite its reference curve against the new cell. After one complete cycle, percentage readings stabilise.