Nokia 8800E BL-5U Replacement Battery 3.7V 750mAh

Nokia 8800E / 8900E Series — 3.7V Li-ion Replacement Battery (BL-5U)

The BL-5U is a 3.7V Li-ion cell rated at 750mAh (2.78Wh), replacing the original battery in the Nokia 8800E, 8900E, and 8900i. These are slim luxury handsets with tight internal tolerances, so a correctly specced cell matters. This replacement matches the OEM voltage, capacity, and physical footprint at 62.02 × 36.90 × 3.92mm.

• 8800E, 8900E, and 8900i compatibility: All three models share the BL-5U form factor, the same 3.7V charging rail, and the same connector pinout. The BMS on each handset expects the same charge termination voltage, so one cell covers the full range without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the 8800E platform. The BMS accepted the cell, reached full charge termination at 4.2V, and held stable voltage through a complete discharge without tripping the low-voltage cutoff prematurely.
• Fuel gauge recalibration on first use: After fitting, disable any fast-charge accessories for the first full discharge-charge cycle. The fuel gauge IC on these Nokia handsets needs one uninterrupted cycle at standard current to map the new cell's discharge curve before it can report percentage accurately.

Sudden shutdown at 20–30% on the Nokia 8800E after a cell swap

This is a voltage cliff issue, not a capacity fault. The 8800E's modem and display draw a brief current spike that the new cell can't sustain if the fuel gauge IC is still calibrated to the old degraded cell's curve. The phone reads 25% but the actual open-circuit voltage has already dropped below the BMS cutoff threshold under load. One full discharge-charge cycle at standard current resets the coulomb counter and eliminates the premature shutdown.

Phone won't power on after the BL-5U sat in storage for months

Li-ion cells self-discharge in storage. If the BL-5U has been sitting unused, the cell voltage may have dropped below 2.5V — the threshold at which the BMS enters lockout to prevent damage. The phone will show no response to the power button and may not react to a charger immediately. Connect the handset to a low-current USB charger and leave it for 15–20 minutes; the BMS recovery circuit will trickle charge the cell back above 2.7V and release the lockout before resuming normal charging.