Bea-fon SL645 Replacement Battery 3.7V 1300mAh Li-ion

Bea-fon SL645 / SL645 Plus — 3.7V Li-ion Replacement Battery (ICP5/44/55)

This is a 3.7V, 1300mAh (4.81Wh) Li-ion cell for the Bea-fon SL645 and SL645 Plus mobile phones. It replaces part number ICP5/44/55 and fits both model variants. Install it when the original cell no longer holds a charge or the phone shuts down unexpectedly under load.

• SL645 and SL645 Plus compatibility: Both models share the same battery bay dimensions, connector pinout, and BMS communication protocol. One cell covers both variants — no modification needed.
• Bench tested on actual hardware: We cycled this cell through a full discharge-charge sequence on the SL645 platform. The BMS accepted the cell without fault codes, and the charge IC reached termination voltage cleanly at 4.2V.
• First-cycle fuel gauge reset: After installation, disable any fast-charge mode and run one complete discharge down to auto-shutoff, then charge uninterrupted to 100%. This gives the fuel gauge IC a clean reference curve against the new cell before high-current charging sessions begin.

Sudden shutdown at 20–30% on the SL645 after a cell swap

The SL645's fuel gauge IC stores a discharge curve calibrated to the original cell. A new cell with a slightly different internal resistance profile causes the IC to misread remaining capacity. When the phone places a load spike — screen on, call active, radio polling — the actual cell voltage drops below the cutoff threshold before the reported percentage reaches zero. The phone shuts down even though the display showed charge remaining. One full uninterrupted discharge-to-shutoff cycle followed by a full charge resets the coulomb counter and corrects this behaviour.

Phone not powering on after the replacement cell sat in storage

Li-ion cells self-discharge during storage. If the cell voltage has dropped below approximately 2.5V, the BMS enters a lockout state and blocks current flow to protect the cell from damage. The phone will not respond to the power button or show any charging indicator initially. Connect to a charger and leave it for 15–20 minutes without pressing anything — the charge IC will trickle current into the cell until voltage rises above the BMS re-enable threshold, after which normal charging resumes.