Samsung SGH-Z300 Compatible Battery 3.7V 750mAh ST4309VE

Samsung SGH-Z300 Series — 3.7V Li-ion Replacement Battery (ST4309VE)

This is a 3.7V, 750mAh Li-ion cell replacing the original ST4309VE battery in Samsung's SGH-Z300 clamshell phone. It also fits the SGH-Z308, ZM60, and ZM-60 variants that share the same connector and BMS handshake. Dimensions are 66.21 × 42.34 × 6.97mm — confirm your original against those before ordering.

• SGH-Z300, Z308, ZM60 fitment: These four models share the same battery bay dimensions, positive terminal orientation, and BMS communication protocol. The ST4309VE part number covers the entire group — no separate SKU exists for each variant.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on Z-series hardware. The BMS accepted charge handshake on the first connect, held the 4.2V charge ceiling cleanly, and triggered low-voltage cutoff at the expected threshold without false trips.
• First-cycle fuel gauge reset: After fitting this cell, run one complete discharge down to automatic shutdown, then charge uninterrupted to 100% before use. The SGH-Z300's fuel gauge IC was calibrated to the old cell's discharge curve — skipping this step causes the percentage counter to read inaccurately for weeks.

Why the SGH-Z300 reports wrong battery percentage after a cell swap

The SGH-Z300 uses a coulomb counter IC that builds its fuel gauge model from accumulated charge and discharge data on the installed cell. When you swap in a new cell, that learned curve no longer matches the new cell's actual capacity and impedance. The phone uses the old data until it completes at least one full discharge-charge cycle with the new cell. Until recalibration happens, the percentage display can read 40% and drop to zero without warning.

Sudden shutdown at 20–30% battery remaining

This is a voltage cliff failure, not a capacity problem. The Z300's display and radio draw simultaneous current spikes — particularly during a call with the backlight active — that the cell cannot sustain if its internal impedance is high. Voltage drops below the modem's minimum operating threshold in milliseconds and the phone cuts off. If this happens on a new cell, run the full recalibration cycle first. If it persists after one full cycle, check that the terminal contacts are fully seated — a partial connection raises effective impedance and triggers the same collapse at around 3.5V.