HE378 Nokia 3.1A Replacement Battery 3.8V 2800mAh

Nokia 3.1A / TA-1140 / TA-1141 — 3.8V Li-Polymer Replacement Battery (HE378)

This is a 3.8V, 2800mAh Li-Polymer cell replacing the OEM HE378 battery in the Nokia 3.1A smartphone. It fits the TA-1140 and TA-1141 board variants. Capacity matches the original specification so the fuel gauge IC has a consistent reference point for recalibration.

• TA-1140 and TA-1141 compatibility: Both board variants use the same 3.8V power rail, identical connector pinout, and the same BMS handshake protocol — one cell covers both. No hardware modification needed.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a Nokia 3.1A unit. The BMS accepted the cell without fault codes, and charge current stepped down correctly at the top-of-charge threshold.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard current. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before any high-current charging session begins.

Sudden shutdown at 20–30% on the Nokia 3.1A after a cell swap

The Nokia 3.1A shuts down abruptly at 20–30% because the fuel gauge IC is still reading the discharge curve of the old, degraded cell. The new cell has a steeper voltage drop under modem and screen load than the calibration table expects, so the IC doesn't see the voltage cliff coming. The phone cuts out before it reports 0%. One full discharge-charge cycle at standard current resets the coulomb counter and brings the percentage readout back in line with actual cell state.

Phone not powering on after the replacement cell sat in storage

Li-Polymer cells self-discharge in storage, and if the cell drops below 2.5V the BMS enters a protection lockout to prevent damage. The Nokia 3.1A will show no response — no boot screen, no charging indicator — when it receives the cell in this state. Plug in a known-good charger and leave it connected for 15–20 minutes without pressing the power button. The charge IC trickle-charges the cell back above the BMS re-enable threshold, typically around 2.9V, at which point the device will begin a normal boot sequence.