Apple iPhone 2G Replacement Battery 3.7V 2250mAh Li-Polymer

Apple iPhone 2G — 3.7V Li-Polymer 2250mAh Replacement Battery

This is a 3.7V lithium-polymer replacement battery rated at 2250mAh (8.33Wh) for the Apple iPhone 2G 4GB and 8GB. It replaces the original cell when capacity has degraded, charging has become erratic, or the phone no longer holds a usable charge. Voltage and form factor match the original specification.

• iPhone 2G 4GB and 8GB compatibility: Both models share the same battery bay geometry, connector pinout, and charge IC handshake — one cell fits both. No modification required for either variant.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the iPhone 2G platform, monitoring BMS cutoff at the low-voltage threshold and confirming charge acceptance through the device's onboard charge controller.
• Fuel gauge recalibration after swap: After installing this cell, run one full discharge down to automatic shutdown, then charge uninterrupted to 100% before normal use. The iPhone 2G fuel gauge IC maps its percentage readings against a learned discharge curve — skipping this step causes the reported percentage to drift against actual cell state.

Why the iPhone 2G shuts down suddenly at 20–30% after a cell swap

The original fuel gauge IC stores a discharge curve calibrated to the old, degraded cell. A new cell has a steeper voltage cliff at the low end — the device reads 25% but the actual cell voltage drops below the modem's minimum rail faster than the IC expects. The processor triggers an emergency shutdown before the percentage reaches zero. One full discharge-to-cutoff cycle followed by a full charge lets the IC rebuild its model against the new cell's actual curve.

Phone warm near the battery during the first charge after replacement

A new high-impedance cell produces more heat during initial charge cycles than a broken-in cell does. The charge IC on the iPhone 2G applies a constant-current phase until the cell reaches approximately 4.2V, and internal resistance on a fresh cell converts more of that current to heat. This is normal and typically reduces after two or three full cycles. If the phone becomes hot to the touch rather than warm, disconnect it and check seating of the battery connector.