Samsung X300 Replacement Battery 3.7V 600mAh Li-ion

Samsung X300 — 3.7V Li-ion Replacement Battery

This is a 3.7V, 600mAh lithium-ion cell built to fit the Samsung X300 flip phone. The X300 is a compact mid-2000s handset, and original batteries at this age have typically lost 40–60% of their original capacity. This replacement restores the phone to its original operating voltage and charge cycle behaviour.

• X300 platform fit: The X300 uses a single-cell 3.7V Li-ion pack with a compact footprint — 49.50 × 33.80 × 4.70mm. This cell matches that physical envelope and voltage rail exactly. No connector modification is needed.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the X300 platform. The onboard charge IC accepted the cell without rejection, and the BMS held steady through both low-load standby and higher-draw screen-on states.
• Fuel gauge recalibration on first use: After fitting this cell, run one full discharge down to auto-shutdown, then charge uninterrupted to 100% before regular use. The X300's fuel gauge IC was calibrated to your old, degraded cell — it needs one complete cycle to remap its percentage readings to the new cell's actual discharge curve.

Why the X300 reports wrong battery percentage after a cell swap

The X300 tracks charge state using a fuel gauge IC that builds a model of the cell's discharge curve over time. When you swap to a new cell, that stored model still reflects the old, degraded battery — not the fresh one. The result is percentage readings that jump around or show full charge well before the cell is actually full. One complete discharge-to-shutdown followed by a full uninterrupted charge forces the IC to relearn the curve against the new cell. After that single cycle, percentage reporting stabilises.

Sudden shutdown on the X300 with 20–30% still showing

This happens when the cell voltage drops sharply under load — a behaviour called a voltage cliff. Even with charge remaining, the cell can't sustain the minimum voltage the phone's processor needs during screen-on or active use bursts. On a worn original cell this is common, but it can also occur briefly with a new cell if the fuel gauge IC hasn't recalibrated yet. Run one full discharge cycle so the IC maps the new cell's actual low-voltage threshold. If shutdowns continue after that cycle, check that the battery contacts on the phone are clean and making full contact — target at least 3.6V measured at the terminals under light load.