Olympia Happy II Replacement Battery ICP423450 3.7V 900mAh

Olympia Happy II / 2218 — 3.7V Li-ion Replacement Battery (ICP423450)

This is a 3.7V, 900mAh Li-ion cell for the Olympia Happy II and 2218 mobile phones. It replaces OEM part ICP423450 when the original cell no longer holds a charge or fails to power the handset. Dimensions are 53.35 × 36.80 × 4.50mm — verify against your existing cell before fitting.

• Happy II and 2218 compatibility: Both models share the same PCB connector, cell footprint, and 3.7V nominal voltage rail. The BMS handshake is identical across the two, so this cell fits either without hardware modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Happy II platform. The BMS accepted the cell without fault flags, and protection cutoffs triggered correctly at both low-voltage and over-charge thresholds.
• Fuel gauge recalibration on first use: On first use after fitting, disable any fast-charge mode and run one full discharge-to-charge cycle. This lets the fuel gauge IC build an accurate discharge curve against the new cell before high-current charging is applied to an uncalibrated cell.

Sudden shutdown at 20–30% on the Olympia Happy II after a cell swap

This happens because the phone's fuel gauge IC is still using the discharge curve it mapped to the old, degraded cell. When the new cell hits a voltage point the IC associates with near-empty, it pulls the shutdown signal even though real capacity remains. The fix is a full uninterrupted discharge to auto-off, followed by a full charge without interruption. After one complete cycle the coulomb counter recalibrates and the percentage readout stabilises.

Phone not powering on after the replacement cell sat in storage

Li-ion cells self-discharge in storage. If the cell dropped below approximately 2.5V, the BMS enters lockout to prevent damage and will not pass current to the phone. Connect the phone to a wall charger — not a USB hub — and leave it for 15–20 minutes without pressing the power button. Most BMS circuits on this class of phone require a trickle pre-charge pulse to exit lockout before normal charging can resume. If the charge LED does not activate within 30 minutes, check the charger output is at least 5V 500mA.