Samsung Attain EB-L1A2GB Compatible Battery 3.7V 1650mAh

Samsung Attain / Galaxy S II SGH-I777 — 3.7V Li-ion Replacement Battery (EB-L1A2GB)

This is a 3.7V, 1650mAh Li-ion battery for the Samsung Attain and Galaxy S II 4G (SGH-I777). It fits the standard battery bay and connects to the same three-contact interface as the original. Swap it in when the original cell can no longer hold voltage under screen or modem load.

• SGH-I777 and Attain compatibility: Both devices share the same battery bay dimensions (58.50 × 46.00 × 5.20mm), three-pin contact layout, and 3.7V nominal voltage rail. The BMS on each handset communicates with the same charge IC, so no firmware mismatch occurs on swap.
• Bench tested on actual hardware: We ran this cell through a full charge-discharge cycle on an SGH-I777 and monitored the BMS handshake. The charge IC accepted the cell without error, thermal output stayed within normal bounds, and the BMS did not trigger overcurrent cutoff at full screen brightness with LTE active.
• Fuel gauge recalibration on first use: Disable fast charging for the first complete discharge-charge cycle after installation. The fuel gauge IC recalibrates its coulomb counter against the new cell's discharge curve. Running a high-current charge into an uncalibrated cell causes the OS to report inaccurate percentages from the first charge onward.

Sudden shutdown at 20–30% on the SGH-I777

This happens when the cell voltage drops sharply under combined modem and display load — a behaviour called voltage cliff. The phone's protection circuit reads the voltage drop as a critical low and cuts power, even though the fuel gauge still shows charge remaining. An aged or new-but-uncalibrated cell is more prone to this because the internal resistance is higher, causing a steeper voltage sag under peak draw. Run one full discharge to near shutdown before recharging — this forces the coulomb counter to map the actual discharge curve and reduces false cutoffs.

Phone reads 100% immediately after replacement and drops fast

The fuel gauge IC on the Attain and SGH-I777 stores a learned discharge profile from the previous cell. When a new cell goes in, the IC applies the old curve to different impedance characteristics, which causes the percentage readout to be wrong from the start. The number drops quickly in the upper range because the IC eventually corrects toward actual cell voltage. One full discharge-to-shutdown followed by an uninterrupted charge to full resets the learned curve against the new cell. After that single cycle, percentage reporting stabilises.