Samsung SGH-S300 Replacement Battery BST1318SE 3.7V 850mAh

Samsung SGH-S300 Series — 3.7V Li-ion Replacement Battery (BST1318SE)

This is a 3.7V, 850mAh Li-ion replacement battery for the Samsung SGH-S300, SGH-S307, and SGH-S308 mobile phones. It replaces OEM part numbers BST1318SE, BSL1315LE, and BST1318DE. If the original cell has degraded, swollen, or stopped holding a charge, this unit restores power to the handset.

• SGH-S300 / S307 / S308 compatibility: All three models share the same battery bay dimensions, 3.7V nominal rail, and connector pinout — the same cell fits all without modification to contacts or housing.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the SGH-S300 platform. The BMS accepted charging without tripping overcurrent protection, and voltage held steady through full discharge without an early cutoff event.
• Fuel gauge recalibration on first use: On first installation, run one full discharge down to auto-shutdown, then charge uninterrupted to 100%. The SGH-S300's fuel gauge IC is calibrated to the original cell's discharge curve — one complete cycle resets the coulomb counter against the new cell's actual capacity.

Sudden shutdown at 20–30% on the SGH-S300 after a cell swap

This happens because the phone's fuel gauge IC still references the discharge curve of the old, degraded cell. The new cell has a steeper voltage cliff at low state-of-charge — the phone's power IC sees terminal voltage drop below its cutoff threshold before the percentage counter reaches zero. It is not a fault with the replacement cell. One full discharge-charge cycle gives the coulomb counter enough data to remap the curve against the new cell, and the shutdowns stop.

Phone not powering on after the replacement battery sat in storage

Li-ion cells self-discharge in storage. If the cell voltage has dropped below approximately 2.5V, the BMS trips its deep-discharge lockout and blocks current flow to protect the cell from damage. The phone will show no response — no boot screen, no charging indicator. Connect the handset to a charger and leave it for 15–20 minutes without attempting to power it on. Once the BMS detects voltage has recovered above its reinitialisation threshold, the charging indicator will appear and normal operation resumes.