Bea-fon T850 Replacement Battery 3.7V 1200mAh Li-ion

Bea-fon T850 / SL320 — 3.7V Li-ion Replacement Battery (T850)

This 3.7V 1200mAh (4.44Wh) Li-ion cell replaces the original battery in the Bea-fon T850 and SL320 mobile phones. Both are candybar-style handsets that share the same battery bay dimensions and connector. Swap this in when the original cell no longer holds adequate charge for calls and messaging.

• T850 and SL320 compatibility: Both models use the same 60.00 × 43.80 × 4.50mm form factor, identical three-pin connector, and matching voltage rail — so one cell fits both without modification.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the T850 platform. The BMS accepted charge handshake on the first connect, and the protection circuit tripped correctly at low-voltage threshold — no false cutoffs mid-cycle.
• Fuel gauge recalibration on first use: After fitting this cell, disable fast charging and run one complete discharge-to-charge cycle before normal use. The T850's fuel gauge IC was calibrated to your old cell's discharge curve — letting it re-map against the new cell first prevents erratic percentage readings from day one.

Sudden shutdown at 20–30% on the Bea-fon T850 after a cell swap

This happens because the fuel gauge IC still holds the discharge curve from the old, degraded cell. The new cell hits a steeper voltage cliff under modem or screen load than the IC expects, so the phone interprets a rapid voltage drop as imminent shutdown and cuts power. The fix is one full discharge-charge cycle with the screen on and mobile data active — this forces the coulomb counter to relearn the actual capacity endpoints. After that cycle, the phone should report percentage accurately down to the correct low-voltage cutoff near 3.2V.

Phone warm near the battery compartment during first charge after replacement

A new cell arrives with higher internal impedance than a broken-in one. During the first charge, the T850's charge IC pushes current into that higher-impedance cell, which converts more energy to heat than usual. This is normal for the first one to two cycles and settles as the cell conditions. If the device stays warm beyond the third full charge, check that nothing is blocking the back panel and that ambient temperature is below 35°C — heat above that during charging accelerates electrolyte degradation in the new cell.