BLU N4S75T Deejay Touch Replacement Battery 3.7V 800mAh

BLU Deejay Touch — 3.7V Li-ion Replacement Battery (N4S75T)

This is a 3.7V, 800mAh Li-ion replacement battery for the BLU Deejay Touch and related BLU handsets. It fits the Deejay Touch, Tattoo Mini TV, Deejay II, and Lindy, among others. OEM part numbers N4S75T and N4S75J both cross-reference to this cell.

• Multi-model BLU fit: These BLU handsets share a common 3.7V single-cell architecture with the same physical footprint and connector orientation. The BMS handshake requirements across the Deejay and Lindy lines are identical, so one cell services the full group without modification.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the Deejay Touch platform. The BMS accepted charge current without cutoff events, and the protection circuit tripped correctly at the low-voltage threshold before cell damage could occur.
• Fuel gauge recalibration on first use: After swapping this cell in, disable fast charging and run one complete discharge-to-charge cycle before normal use. The fuel gauge IC on these BLU devices calibrates its coulomb counter against the new cell's discharge curve — skipping this step causes the percentage reading to jump erratically for the first several days.

Why the Deejay Touch reports wrong battery percentage after a cell swap

The fuel gauge IC stores a learned discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches the actual voltage-to-capacity relationship of the replacement. The IC reads voltage and maps it against the old data, so the displayed percentage is wrong until it relearns. One full discharge below 5% followed by an uninterrupted charge to 100% forces the coulomb counter to reset and rewrite the curve against the new cell.

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 did not anticipate. The phone reads 25% but the cell is already at or near the BMS cutoff threshold under real current draw. It is not a faulty battery — it is an uncalibrated fuel gauge sending the OS a stale percentage. Run two full discharge-charge cycles and check whether the shutdowns move toward a lower reported percentage each time. If the phone still cuts out above 15% after three cycles, confirm charge voltage reaches 4.2V at the end of each charge.