Sharp SH903i Replacement Battery 3.7V 650mAh Li-ion

Sharp SH903i / SH902ISL — 3.7V Li-ion Replacement Battery (SH09)

This is a 3.7V, 650mAh Li-ion cell for the Sharp SH903i and SH902ISL candybar phones sold in the Japanese domestic market. It replaces the original SH09 battery when the existing cell can no longer hold charge through a normal day of use. Dimensions are 44.48 × 38.60 × 4.18mm — measure your original before ordering if you are unsure.

• SH903i and SH902ISL shared platform: Both handsets run the same battery bay dimensions, connector pinout, and BMS handshake protocol, which is why a single cell covers both models without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the SH903i platform. The BMS accepted the cell without error flags, and the protection circuit responded correctly to over-discharge cutoff at the expected low-voltage threshold.
• Fuel gauge recalibration on first use: On first installation, run one complete discharge to automatic shutoff, then charge uninterrupted to 100% before normal use. The SH903i fuel gauge IC maps its percentage readings against the discharge curve it sees on that first full cycle — skipping this step causes erratic percentage jumps for days afterward.

Sudden shutdown at 20–30% on the SH903i after a cell swap

The SH903i's processor and display draw a combined current spike during screen-on events that the fuel gauge IC cannot always predict from a freshly installed cell. If the new cell's internal impedance is slightly higher than the original, terminal voltage dips sharply under that load — the protection circuit reads it as a low-voltage condition and cuts power even though the state-of-charge counter still shows 20–30%. One full discharge-charge calibration cycle usually resolves this. If shutdowns continue past two cycles, check that the battery contacts in the bay are clean and making full contact.

Phone will not power on after the replacement battery sat in storage

Li-ion cells self-discharge in storage, and if the SH09 cell dropped below roughly 2.5V per cell before installation, the BMS enters a lockout state to prevent further discharge damage. The phone will show nothing when you press power — no logo, no vibration. Connect the charger and leave it for 15–20 minutes without pressing any buttons; the charge IC trickle-charges the cell back above the BMS re-enable threshold, typically around 2.9V, at which point the phone will power on normally.