Samsung SGH-M608B Replacement Battery 3.7V 650mAh Li-ion

Samsung SGH-M608B — 3.7V Li-ion Replacement Battery

This is a 3.7V, 650mAh Li-ion replacement battery for the Samsung SGH-M608B mobile phone. It slots into the original battery bay and restores power to the handset's calling and messaging functions. Capacity matches the original 650mAh cell specification.

• SGH-M608B cell format: The M608B uses a compact single-cell Li-ion pack running a 3.7V nominal rail. The connector and cell dimensions are matched to the original battery bay — no modification needed. The BMS communicates charge state directly to the phone's power management IC.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the SGH-M608B platform. The BMS accepted charge current from the phone's internal charge IC without fault, and cutoff triggered correctly at the low-voltage threshold.
• Fuel gauge recalibration after install: After fitting this replacement, run one full discharge to automatic shutdown before recharging completely. The SGH-M608B's fuel gauge IC was calibrated to the original cell's discharge curve — skipping this step causes erratic percentage readings until the IC maps the new cell's actual capacity.

Sudden shutdown at 20–30% on the SGH-M608B after cell replacement

This is a voltage cliff issue, not a capacity defect. At 20–30% state of charge, the new cell's voltage drops faster than the fuel gauge IC predicts, because the IC is still working from the old cell's discharge curve. When voltage falls below the phone's minimum operating threshold — around 3.2V under screen or call load — the system shuts down even though the percentage display still shows charge remaining. One full discharge-to-shutdown cycle followed by a full charge corrects the IC's reference curve. After that cycle, shutdowns at falsely reported percentages should stop.

SGH-M608B not powering on after the replacement battery sat in storage

Li-ion cells that sit uninstalled drop voltage over time through self-discharge. If the cell has fallen below approximately 2.5V per cell, the BMS enters lockout mode to prevent unsafe charging of a deeply discharged cell. The phone will not power on and may not show a charging indicator at all. Connect the phone to a charger and leave it undisturbed for 20–30 minutes — the charge IC will attempt a low-current trickle recovery phase. If the charging indicator appears within that window, the cell is recovering; allow a full charge cycle before powering on.