Samsung SCH-U640 Replacement Battery AB663450GZ 3.7V 1300mAh

Samsung SCH-U640 Convoy Series — 3.7V Li-ion Replacement Battery (AB663450GZ)

This is a 3.7V, 1300mAh Li-ion replacement battery for the Samsung SCH-U640 and SCH-U640 Convoy. It also fits the Convoy 2 U660 and SCH-U660. The AB663450GZ cell matches the original form factor at 52.30 × 33.20 × 6.50mm and drops into the stock battery bay without modification.

• Convoy and U660 platform fit: The SCH-U640, SCH-U640 Convoy, and SCH-U660 Convoy 2 all share the same battery bay dimensions and connector pinout. One cell covers the full Convoy lineup without adapter or rewiring.
• Bench tested on actual hardware: We ran this cell on a U640 unit and confirmed the BMS handshake with the charge IC. The protection circuit tripped correctly at low-voltage cutoff and resumed charging without manual reset once voltage recovered above the reinitialisation threshold.
• Fuel gauge recalibration on first cycle: After installing a new cell, run one full discharge to automatic shutoff, then charge uninterrupted to 100% before normal use. The phone's coulomb counter is calibrated to the old cell's discharge curve — skipping this step causes the OS to report inaccurate percentages from day one.

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

This is a voltage cliff failure, not a capacity problem. Under peak modem load or screen-on draw, the new cell's internal resistance causes voltage to sag below the phone's cutoff threshold before the display percentage reaches zero. The fuel gauge IC hasn't yet mapped the new cell's discharge curve, so it reports a percentage that no longer matches actual cell voltage. Run one full discharge-charge cycle without interruption — after that single calibration pass, the shutoff threshold aligns with the real voltage floor.

Phone won't power on after the replacement battery sat in storage

Li-ion cells self-discharge during storage. If the cell drops below approximately 2.5V, the BMS enters lockout to prevent damage and the phone shows no response to the power button. Connect the phone to a wall charger — not a PC USB port — and leave it for 15–20 minutes without pressing anything. Most charge ICs on this platform apply a trickle pre-charge to recover a locked-out cell back above the reinitialisation voltage before switching to standard CC/CV charging.