Bea-fon SL340 Replacement Battery 3.7V 1300mAh Li-ion

Bea-fon SL340 / SL750 — 3.7V Li-ion Replacement Battery (SL340, SL750)

This 3.7V, 1300mAh Li-ion cell replaces the original battery in the Bea-fon SL340 and SL750 mobile phones. Both models use the same cell format, connector, and BMS interface, so one part covers either handset. Capacity is 4.81Wh — matching the original specification.

• SL340 and SL750 compatibility: Both phones share the same battery bay dimensions (60.00 × 43.80 × 4.50mm), connector pinout, and charge management handshake. The cell slots into either device without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the SL340 platform. The BMS accepted the charge IC handshake without fault codes, and cell voltage held stable across the full discharge curve under voice-call load.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-charge cycle before resuming normal use. The fuel gauge IC on these phones calibrates its coulomb counter against the actual cell discharge curve — doing this first prevents the erratic percentage readings that follow a cell swap.

Why the SL340 reports wrong battery percentage after a cell swap

The SL340 and SL750 use a fuel gauge IC that tracks charge state by counting coulombs in and out of the original cell. When a new cell goes in, the IC still references the old discharge curve. The result is percentage readings that drift — often showing 100% well past what the cell can sustain. One full discharge to automatic power-off, followed by an uninterrupted charge to 100%, forces the IC to re-anchor its curve to the new cell. After that single cycle, percentage accuracy normalises.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops sharply under the load of an active call or screen-on event — a voltage cliff the fuel gauge did not predict because it was calibrated to the old cell. The BMS trips at the lower threshold before the reported percentage reaches zero, cutting power without warning. Run the phone down to automatic shutdown, then charge fully without interruption. After one complete cycle the fuel gauge maps the new cell's actual cliff point and the shutdowns stop. If the issue continues past two cycles, check that the cell resting voltage reads at least 3.6V immediately after a full charge.