Nokia 800 Tough BPCNTBY001B Replacement Battery 3.8V 2100mAh

Nokia 800 Tough / TA-1186 — 3.8V Li-Polymer Replacement Battery (BPCNTBY001B)

This is a 3.8V, 2100mAh Li-Polymer replacement battery for the Nokia 800 Tough rugged smartphone (models TA-1186 and TA-1186/DS). It replaces OEM part numbers BPCNTBY001B and BV-5D. The cell dimensions are 82.50 × 40.00 × 4.50mm — measure your original before ordering if you are unsure.

• 800 Tough / TA-1186 compatibility: Both TA-1186 and TA-1186/DS share the same battery bay, connector pinout, and BMS handshake protocol — one cell covers both variants without modification.
• Bench tested on actual hardware: We cycled this cell in a TA-1186 unit and confirmed full BMS handshake, charge termination at 4.35V, and stable discharge under screen-on and modem-active load.
• Fuel gauge recalibration on first use: After fitting this cell, disable fast charging and run one complete discharge down to auto-shutdown, then charge to 100% on standard current. This gives the coulomb counter a clean reference curve before high-current charging begins on the new cell.

Sudden shutdown at 20–30% on the Nokia 800 Tough

This is a voltage-cliff failure, not a capacity problem. At 20–30% state-of-charge, the cell voltage drops sharply under combined modem and display load — the BMS cuts power before the OS can log a low-battery event. The fuel gauge IC is still running its calibration curve from the old cell, so the percentage shown is inaccurate. One full discharge-to-shutdown cycle followed by a full charge resets the coulomb counter and resolves this on most units.

Phone won't power on after the battery sat in storage

Li-Polymer cells self-discharge in storage. If the cell drops below approximately 2.5V, the BMS enters a lockout state and blocks normal charging to prevent thermal runaway on a critically depleted cell. The phone will show no charge indicator and will not respond to a standard charger. Connect to a 5V USB source and leave it for 20–30 minutes — the charge IC applies a trickle current that brings the cell above the BMS recovery threshold, after which normal charging resumes.