About this replacement
BLU Studio 5.5S / D630U / D630L — 3.8V Li-Polymer Replacement Battery (C786340235T)
This is a 3.8V, 2100mAh Li-Polymer battery for the BLU Studio 5.5S, D630U, and D630L smartphones. It replaces OEM part number C786340235T. The battery slots into the same footprint as the original — 78.00 x 63.45 x 4.00mm — and connects to the same charge IC and fuel gauge circuit.
- Studio 5.5S, D630U, and D630L compatibility: These three model numbers share the same battery bay dimensions, connector pinout, and BMS handshake protocol. The fuel gauge IC on all three reads the same cell chemistry signature, so the replacement communicates charge state correctly across all variants.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a D630U. The BMS accepted the new cell on the first charge cycle, protection thresholds triggered at expected voltage levels, and the fuel gauge began tracking state-of-charge within one full cycle.
- First-cycle calibration on the Studio 5.5S: On first use after installation, disable fast charging and let the phone complete one full discharge-to-charge cycle. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current charging pushes load into an uncalibrated cell.
Why the Studio 5.5S reports the wrong battery percentage after a cell swap
The fuel gauge IC on the D630-series board stores a learned discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches actual cell behaviour, so the reported percentage drifts from true state-of-charge. The IC needs at least one complete discharge cycle — from full to auto-shutdown — followed by a full charge to re-anchor its coulomb counter. After that cycle, percentage readings stabilise and track the new cell accurately.
Sudden shutdown at 20–30% on the replacement cell
This happens when the cell voltage drops sharply under modem or screen load — a voltage cliff the fuel gauge didn't predict because it was still calibrated to the old cell. The BMS trips the output before the displayed percentage reaches zero. It is not a faulty battery. Run one full discharge cycle without interrupting it, then charge to 100%. After recalibration, the fuel gauge tracks the cliff correctly and the premature shutdowns stop. Confirm the cell is holding above 3.5V under load after that cycle.