About this replacement
Samsung SCH-i859 / SGH-I728A / SGH-I740 — 3.7V Li-ion Replacement Battery (AB514757BC)
This is a 3.7V, 1600mAh Li-ion replacement battery for the Samsung SCH-i859, SGH-I728A, and SGH-I740 smartphones. It uses OEM part number AB514757BC and slots directly into the original battery bay. Capacity is rated at 5.92Wh from the cell forward — no inflated figures.
- SCH-i859, SGH-I728A, SGH-I740 platform fit: All three models share the same 3.7V battery rail, AB514757BC connector pinout, and BMS handshake protocol — one cell covers all three without adapters or firmware changes.
- Bench tested on actual hardware: We cycled this cell through full charge and discharge on the SCH-i859 platform. The BMS accepted the cell on first connection, charge termination triggered correctly at 4.2V, and protection circuitry tripped as expected under an over-discharge load condition.
- First-cycle fuel gauge recalibration: On first use after installation, disable fast charging and run one complete discharge-to-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging begins against an uncalibrated reference.
Sudden shutdown at 20–30% on the SCH-i859 after a cell swap
The SCH-i859 fuel gauge IC holds a learned discharge curve from the original cell. When a new cell goes in, the IC still references the old curve — so it misreads remaining voltage headroom under load. Screen-on or modem transmission draws enough current to push the new cell past its voltage floor before the OS sees it coming. The phone shuts off even though the percentage display says 25–30%. One full discharge cycle down to automatic cutoff, followed by a full charge to 100%, forces the coulomb counter to reset against the new cell's actual capacity.
USB charging not starting after the phone sat in storage discharged
If the AB514757BC cell drops below approximately 2.5V during long storage, the BMS enters a lockout state and blocks normal charging current. The phone will not respond to a USB cable and shows no charge indicator. To recover the cell, apply a low-current trickle source — some wall chargers do this automatically in a pre-charge stage — and hold it connected for 15–20 minutes before the BMS releases the lockout. Once voltage climbs above 3.0V, standard charge current resumes and the device powers on normally.