Samsung SGH-N620 Replacement Battery BST0698DE 3.7V 900mAh

Samsung SGH-N620 Series — 3.7V Li-ion Replacement Battery (BST0698DE)

This is a 3.7V, 900mAh Li-ion cell that replaces the original BST0698DE and BST0698SE batteries in early-2000s Samsung compact mobile phones. It fits the SGH-N620, SGH-N600, SGH-N628, and SGH-K90. Each cell ships at partial charge — top it off before first use.

• SGH-N620, N600, N628, K90 compatibility: These four models share the same battery bay dimensions, 3.7V nominal rail, and BST-series connector pinout. The BMS handshake on all four accepts the same charge termination signal, so one cell covers the full group without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on an SGH-N620 unit. The BMS hit charge termination correctly at 4.2V, and the protection circuit tripped at the expected low-voltage cutoff without error flags.
• Fuel gauge recalibration on first cycle: After fitting the new cell, run one full discharge down to automatic shutdown, then charge uninterrupted to 100%. The phone's fuel gauge IC was calibrated to the old cell's discharge curve — one complete cycle rewrites the reference baseline so percentage readings track accurately.

Why the SGH-N620 reports wrong battery percentage after a cell swap

Samsung's fuel gauge IC on the N620 stores a learned discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches actual cell chemistry, so the percentage display drifts or jumps. The IC needs a full discharge-to-shutdown followed by an uninterrupted charge to 100% to rewrite its internal reference. Until that cycle completes, readings can be off by 15–25%. After one full cycle, the gauge stabilises and tracks the new cell accurately.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops sharply under the load of an active call or backlit display — a voltage cliff the fuel gauge doesn't anticipate. The phone's protection circuit reads the sag as a low-voltage event and cuts power before the displayed percentage reaches zero. It's not a faulty cell — it means the fuel gauge IC hasn't finished recalibrating against the new cell's discharge curve. Run one complete discharge-to-shutdown and full recharge cycle. After that, the gauge accounts for load-induced sag and shutdown moves to the correct threshold near 3.0V per cell.