BLU Energy X Compatible Battery 3.8V 3900mAh C816105400L

BLU Energy X / E010Q — 3.8V Li-Polymer Replacement Battery (C816105400L)

This is a 3.8V, 3900mAh Li-Polymer cell that replaces the original battery in the BLU Energy X and E010Q smartphones. It fits the OEM battery slot directly and restores power to calls, messaging, and apps. Capacity matches the factory spec at 14.82Wh.

• Energy X and E010Q compatibility: Both variants share the same battery bay dimensions, connector pinout, and BMS handshake protocol — one cell covers both. The C816105400L part number is consistent across the full Energy X line.
• Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on the Energy X platform. The BMS accepted charge current without rejection, and the protection circuit tripped correctly at low-voltage threshold without hard lockout.
• Fuel gauge recalibration on first cycle: After fitting this cell, disable fast charging and run one complete discharge-to-charge cycle at standard current. The fuel gauge IC needs to map the new cell's discharge curve before it can report accurate percentages — skipping this step causes erratic readings for the first several cycles.

Why the Energy X reports wrong battery percentage after a cell swap

The BLU Energy X uses a coulomb-counting fuel gauge IC that builds its capacity model against the original cell's discharge curve over dozens of cycles. When you install a fresh cell, that learned curve no longer applies. The IC keeps using the old model, so percentage readings can jump or stall — typically appearing full for too long, then dropping fast toward 20%. One full slow-charge cycle forces the IC to re-anchor its zero and full reference points against the new cell chemistry.

Sudden shutdown at 20–30% on the replacement cell

This happens when the modem or display draws a current spike the cell cannot sustain at its present state of charge. Voltage sags below the shutdown threshold — typically around 3.2V under load — before the reported percentage reaches zero. The phone cuts power to protect the circuit even though the gauge shows charge remaining. Run two full discharge-charge cycles and check that shutdown moves closer to 5% or below; if it persists above 15%, confirm the cell seated fully and the connector pins are making clean contact.