About this replacement
BLU Studio X / D750U / D750L — 3.8V Li-Polymer Replacement Battery (C905703210P)
This 3.8V, 2100mAh Li-Polymer cell replaces the original battery in the BLU Studio X, D750U, and D750L smartphones. It matches the OEM dimensions at 88.70 × 57.30 × 3.20mm, fitting the battery bay without modification. Capacity is 7.98Wh, identical to the stock cell these models shipped with.
- Studio X / D750U / D750L compatibility: All three variants share the same battery bay dimensions, connector pinout, and BMS handshake protocol. One cell covers all three without any adapter or wiring change.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the D750U. The BMS accepted the cell on first connection, charge current ramped normally, and the protection circuit tripped correctly at low-voltage cutoff.
- Fuel gauge recalibration on first use: After installation, disable fast charging and run one complete discharge-to-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 sessions begin.
Sudden shutdown at 20–30% on the BLU Studio X after a cell swap
This is a voltage cliff problem, not a capacity problem. The fuel gauge IC is still running the discharge model it built against the old, degraded cell. When the new cell hits a voltage point the old model treated as near-empty, the IC tells the OS the battery is critically low — and the phone shuts down even though usable charge remains. One full discharge-charge cycle without interruption rewrites that model against the new cell. After that cycle, the reported percentage and actual cutoff voltage align correctly.
BLU Studio X not powering on after the replacement cell sat in storage
Li-Polymer cells self-discharge in storage. If this cell dropped below approximately 2.5V per cell during shipping or storage, the BMS will have entered lockout mode to prevent damage. The phone will show no response — no boot screen, no charging indicator. Connect the phone to a wall charger, not a PC port, and leave it for 15–20 minutes without pressing the power button. The charge IC needs to push a small trickle current past the BMS lockout threshold before normal charging resumes. Once the cell reaches around 3.0V, the BMS releases and the charging indicator will appear.