About this replacement
Bea-fon SL720 / SL720i — 3.8V Li-Polymer Replacement Battery (BEA7202145)
This 3.8V, 1500mAh Li-Polymer battery replaces the original cell in the Bea-fon SL720, SL720i, and SL720i_EU001B mobile phones. It matches OEM part number BEA7202145 and fits the 57.00 × 44.00 × 5.00mm battery bay directly. Capacity is rated at 5.7Wh — identical to the factory specification.
- SL720 and SL720i platform fit: The SL720 and SL720i share the same mainboard voltage rail and connector pinout, so one cell covers both variants. The BMS handshake on each device uses the same authentication sequence, and this cell's protection circuit responds correctly to it.
- Bench tested on actual hardware: We cycled this cell on an SL720i mainboard and confirmed the BMS accepted charge from the device's charge IC without fault flags. The protection circuit tripped correctly at low-voltage cutoff and recovered cleanly on reconnect.
- First-cycle fast charge protocol: Disable fast charging for the first complete discharge-to-charge cycle after installation. The SL720's fuel gauge IC is calibrated to the old cell's discharge curve — running fast charge into an uncalibrated cell can skew the coulomb counter and cause percentage drift for the life of the battery.
Why the SL720 reports wrong battery percentage after a cell swap
The SL720 uses a fuel gauge IC that builds its charge model against the discharge curve of the cell it learned on. Swap the cell and that learned curve no longer matches physical reality. The IC will report percentages based on old data until it re-learns the new cell's behaviour. One full discharge from 100% to automatic shutdown, followed by a full charge uninterrupted, forces the coulomb counter to reset against the new cell. After that cycle, percentage reporting stabilises.
Sudden shutdown at 20–30% on the replacement cell
This happens when the cell voltage drops below the modem or screen load threshold faster than the fuel gauge predicts — a voltage cliff the IC didn't anticipate. On the SL720, the modem radio draws peak current during calls or data bursts, and a cell the gauge thinks is at 25% may actually sit at 3.4V under that load, triggering the BMS cutoff. The fix is the same recalibration cycle: discharge fully, charge to 100% without interruption. If shutdown persists below 3.5V open-circuit, the cell's internal resistance is causing the sag — check that the battery contacts are fully seated and free of debris.