About this replacement
BlackBerry 5790 / 5820 Series — 3.7V Li-ion Replacement Battery (ASY-02965-001)
This 3.7V, 1300mAh Li-ion cell replaces the original battery in the BlackBerry 5790, 5810, 5820, and 850 series smartphones. It matches the OEM voltage rail and connector spec for these models. Capacity is 1300mAh (4.81Wh), consistent with the stock cell.
- 5790 / 5810 / 5820 / 850 platform fit: These models share the same battery bay dimensions, 3.7V nominal rail, and BMS handshake protocol — one cell covers the whole lineup without modification.
- Bench tested on actual hardware: We cycled this cell on a 5820 unit and confirmed BMS acceptance, stable charge termination at 4.2V, and no mid-cycle cutoff under combined radio and display load.
- Fuel gauge recalibration after install: After fitting this cell, run one full discharge to auto-off followed by an uninterrupted charge to 100% before enabling fast charging. This lets the fuel gauge IC map its charge curve against the new cell before high-current cycles begin.
Sudden shutdown at 20–30% on the BlackBerry 5790 after a cell swap
The 5790's fuel gauge IC retains the discharge curve it learned from the old, degraded cell. When a fresh cell is installed, the IC underestimates remaining capacity and triggers a low-voltage cutoff well before the cell is actually depleted. The phone reads 20–25%, but the gauge is firing shutdown logic based on a stale voltage-to-capacity map. One complete discharge-charge cycle forces the coulomb counter to resync against the new cell's actual curve and clears the premature cutoff behaviour.
BlackBerry 5790 not powering on after sitting in storage
Li-ion cells left discharged in storage can drop below 2.5V per cell, which triggers BMS lockout — a hard protection state that blocks current flow entirely to prevent cell reversal damage. Plugging in a charger appears to do nothing; the phone won't respond and shows no charging indicator. Connect the device to a wall charger (not USB from a PC) and leave it undisturbed for 20–30 minutes. The BMS recovery circuit needs a sustained trickle current to bring cell voltage above the 2.9V re-enable threshold before normal charging resumes.