About this replacement
NTT DoCoMo F904i / F905i Series — 3.7V Li-ion Replacement Battery (F10 / AAF29105)
This is a 3.7V 750mAh lithium-ion cell built to the F10 battery specification. It fits the NTT DoCoMo F904i, F905i, F906i, F1100, and several additional F-series feature phones. Voltage and physical dimensions match the original: 37 × 39 × 6mm with the same connector orientation.
- F-series platform fit: These models share a common battery bay dimension and the same 3.7V single-cell architecture. The BMS handshake protocol is consistent across the F904i through F906i line, so one cell covers the full group without connector modification.
- Bench tested on actual hardware: We cycled this cell on an F904i unit and monitored BMS cutoff thresholds. The protection circuit held at 2.75V under load and capped charge termination at 4.2V — both within spec for this chemistry.
- Fuel gauge recalibration on first use: On first use after installation, run one full discharge-to-charge cycle before enabling any fast or turbo charging mode. The fuel gauge IC in the F-series phones is calibrated to the old cell's discharge curve — giving it one uninterrupted cycle lets it map the new cell's actual capacity before reporting percentage figures.
Why the F904i reports wrong battery percentage after a cell swap
The F904i uses a coulomb-counter-based fuel gauge IC that builds its capacity model from repeated charge and discharge history. When you install a new cell, the IC still holds the old cell's learned curve in memory. Until it completes at least one full cycle on the new cell, the percentage reading reflects the old model — not actual capacity. This means the phone may show 40% and cut out, or show 15% and keep running. One complete discharge from full charge to auto-off, followed by a full charge to 100%, resets the learned curve against the new cell.
Sudden shutdown at 20–30% on the replacement cell
This happens when the cell voltage drops sharply under the combined load of the display, radio modem, and processor — a voltage cliff the BMS reads as a cutoff event even though the fuel gauge still shows charge remaining. On a fresh cell before calibration, the fuel gauge IC has no accurate model of where that cliff sits, so it cannot warn the OS in time. The fix is the same recalibration cycle described above: one full discharge-charge run gives the coulomb counter enough data to place the low-voltage warning earlier in the discharge curve. After that cycle, shutdowns at 20–30% stop in normal use.