Samsung BlackJack II AB813851CA Replacement Battery 3.7V 1200mAh

Samsung BlackJack II / SGH-i617 — 3.7V Li-ion Replacement Battery (AB813851CA)

This is a 3.7V, 1200mAh Li-ion replacement cell for the Samsung BlackJack II (SGH-i617). It also fits the Stripe and DM-S105. OEM part numbers AB813851CA and AB813851CABSTD both cross-reference to this cell.

• SGH-i617 / Stripe / DM-S105 compatibility: These models share the same battery bay dimensions, 3.7V nominal voltage rail, and contact pad layout. The BMS handshake is identical across the group, so one cell covers all listed variants without modification.
• Bench tested on actual hardware: We cycled this cell through full charge and load discharge on the SGH-i617. The BMS engaged correctly at the low-voltage cutoff, and charge termination fired cleanly at full capacity — no runaway or premature cutoff observed.
• Fuel gauge recalibration on first use: After fitting this cell, run one complete discharge down to automatic shutdown before recharging. The BlackJack II's fuel gauge IC is calibrated to a specific discharge curve — skipping this step leaves the coulomb counter reading against the old cell's curve, which causes percentage jumps and early shutdown warnings.

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

The SGH-i617 runs Windows Mobile with an active radio stack. When the modem transmits, it pulls a short, sharp current spike. A new cell with a slightly different internal resistance profile can drop below the BMS cutoff voltage during that spike — even when the fuel gauge still shows 20–30% remaining. This is a voltage cliff, not a capacity fault. The fix is one full calibration cycle: discharge to shutdown, then charge uninterrupted to 100%. After that cycle, the fuel gauge IC maps the new cell's actual voltage curve and the phantom shutdowns stop.

BlackJack II not powering on after the battery sat in storage

Li-ion cells discharged below approximately 2.5V trigger a BMS lockout — the protection circuit disconnects the cell 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. The charge IC trickle-charges the cell up from the lockout threshold. Once the cell climbs above roughly 3.0V, the BMS re-initialises and the phone boots normally.